fix tikv/tikv#6973

As mentioned in the linked issue, the aim is to implement `!Send` for the `PerfContext` struct.
Although the issue is related to the `tikv/tikv` repo, the concerned `PerfContext` is taken from this repo. 
Due to the rule that "foreign traits can't be implemented on foreign types", it isn't possible to directly implement the `!Send` trait on the `PerfContext` struct. So, either I had to enclose the `PerfContext` within another type and implement `!Send` for the new type (along with implementing all the functions present for `PerfContext`), or directly add the `!Send` implementation, where the struct is defined, i.e, in this repo.  I've taken the second path.
but, there is a problem. `impl !Send` is currently only supported in nightly and not on stable channel.
So, it's necessary to build this crate with nightly toolchain, if this patch is accepted.
Signed-off-by: Govardhan G D <govardhangdg@gmail.com>

* add write thread wait time for perf context

* add multi batch write interface

* add interface set_target_path_id for CompatOptions
Signed-off-by: Little-Wallace <bupt2013211450@gmail.com>

* Add reference counted TableProperties bindings
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Add test for table_properties_rc
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* rustfmt
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Fix a clippy lint
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Various changes from review feedback
Signed-off-by: Brian Anderson <andersrb@gmail.com>

Update travis to bulid with xcode11.3, to catch compile error unique to clang11. Tested with a version of rocksdb with clang11 compile errors and see the error in travis CI: https://travis-ci.org/tikv/rust-rocksdb/jobs/634612576?utm_medium=notification&utm_source=github_statusSigned-off-by: Yi Wu <yiwu@pingcap.com>

Needed by https://github.com/tikv/tikv/pull/6209Signed-off-by: Yi Wu <yiwu@pingcap.com>

Update rocksdb with the following changes:
```
cb7efe6d7 2020-01-08 zbk602423539@gmail.. Add oldest snapshot sequence property (#6228) (#141)
c7d775168 2020-01-07 zbk602423539@gmail.. statistics: make ticker and histogram extendible (#136)
ebec1bd8a 2020-01-07 bupt2013211450@gma.. add multibatch write into memtable (#131)
4dcfb8789 2020-01-07 zbk602423539@gmail.. fix invalid register for .seh_savexmm (#140)
```
Signed-off-by: Yi Wu <yiwu@pingcap.com>

Signed-off-by: qupeng <qupeng@pingcap.com>

Signed-off-by: Yi Wu <yiwu@pingcap.com>

Update rocksdb for master branch with following changes:

Cherry-picking flaky test fix:
```
8c436ff96 2019-12-16 yiwu@pingcap.com     Fix DBFlushTest::FireOnFlushCompletedAfterCommittedResult hang (#6018)
```

Cherry-picking titan iterator fix:
```
74a1cac78 2019-11-25 xy.tao@outlook.com   Fix blob context when db_iter uses seek (#6051)
```

Cherry-picking intra-L0 fixes:
```
193cded5a 2019-11-25 bupt2013211450@gma.. fix unstable unittest caused by #5958 (#6061)
7f67659af 2019-11-25 bupt2013211450@gma.. Fix corruption with intra-L0 on ingested files (#5958)
```

Cherry-picking unordered_write fixes:
```
165702113 2019-11-25 bupt2013211450@gma.. Fix IngestExternalFile's bug with two_write_queue (#5976)
720acf34a 2019-12-16 zbk602423539@gmail.. wait pending memtable writes on file ingestion or compact range (#6113)
380779db1 2019-12-16 siying.d@fb.com      Move pipeline write waiting logic into WaitForPendingWrites() (#5716)
```

Upgrade from rocksdb 6.4.4 to 6.4.6:
```
2c55ed1e3 2019-11-25 myabandeh@fb.com     Bump up the version to 6.4.6
5fe5d4b90 2019-11-25 myabandeh@fb.com     Update HISTORY for SeekForPrev bug fix (#5925)
dee7a8cb6 2019-11-25 myabandeh@fb.com     Fix SeekForPrev bug with Partitioned Filters and Prefix (#5907)
aa28dae99 2019-11-25 anand76@devvm1373... Update HISTORY.md with a bug fix
b626c6a2a 2019-11-25 anand76@devvm1373... Fix data block upper bound checking for iterator reseek case (#5883)
c4801798b 2019-11-25 siying.d@fb.com      Fix a bug of the previous fix.
da1af09f7 2019-11-25 siying.d@fb.com      Bump up the version to 6.4.5
47526f4c9 2019-11-25 siying.d@fb.com      Revert "Merging iterator to avoid child iterator reseek for some cases (#5286)" (#5871)
```
Signed-off-by: Yi Wu <yiwu@pingcap.com>

* fix titan open without cf
Signed-off-by: Connor1996 <zbk602423539@gmail.com>

* change c.h and c.cc for bindgen ffi
Signed-off-by: fredchenbj <cfworking@163.com>

- Update `rand` to v0.7
- Move `crc` to `dev-dependencies`
- Remove `byteorder`
- Replace `tempdir` with `tempfile`
Signed-off-by: koushiro <koushiro.cqx@gmail.com>

* Fix various unsafe declarations

As reported by clippy. These are all cases where a pointer argument is
dereferenced by a declared safe function. The functions are changed to be unsafe
functions. Though some of these functions are declared pub, they all seem to be
related to internal binding matters and appear to be written correctly, just
declared incorrectly, so there shouldn't be any external impact for callers
that aren't using the crocksdb API directly.
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Fix some clippy style lints
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Fix mutability of crocksdb_load_latest_options errptr

This value can be mutated on the C side. Caught by clippy.
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Cleanup some unit-return functions
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Disable a clippy lint
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* make a transmute more typesafe
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Elide a lifetime
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Remove unnecessary unsafe blocks
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Use repr(C) structs of c_void for opaque types.

These represent opaque RocksDB types. They are used behind pointers, but are
also wrapped in other types in the higher-level bindings.

These use the strategy for opaque C types described in the nomicon [1]:
but with the exception that they contain c_void instead of [u8; 0], thus
making them uninstantiable sized types instead of ZSTs.

The c_void documentation publicly recommends using the ZST pattern from the
nomicon, but in private documentation [2] warns about UB from dereferencing
pointers to uninhabited types, which these bindings do.

Additionally, these bindings wrap some these types directly (not through
pointers) and it's impossible to repr(transparent) a ZST, without which the
unsafe casts within are dubious.

[1]: https://doc.rust-lang.org/nomicon/ffi.html#representing-opaque-structs
[2]: https://doc.rust-lang.org/nightly/src/core/ffi.rs.html#28Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Apply repr(transparent) to various unsafe-cast wrappers

These are wrappers of opaque FFI types, and pointers are being unsafely cast
between the two. repr(transparent) is probably needed to make this well-defined.
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Replace mem::transmute with pointer casts

Slightly more typesafe, and more explicit about what's being cast.
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Replace more mem::transmute with casts
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Remove a no-op mem::transmute
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Remove is_power_of_two

std contains a branchless bitmagic version of this function
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Add clippy makefile target
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Add clippy to CI
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Fix types in memcpy

This code is copying from c_void pointers when it should be copying
from byte pointers.

Fortunately c_void and u8 have the same size, but I don't know if that is
guaranteed.
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Update src/rocksdb.rs
Co-Authored-By: kennytm <kennytm@gmail.com>
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Install clippy on travis
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Adjust clippy lints for CI toolchain
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* Make a typesafe cast
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* rustfmt
Signed-off-by: Brian Anderson <andersrb@gmail.com>

Found via valgrind.
Signed-off-by: Brian Anderson <andersrb@gmail.com>

* fix titan cf options for create_cf
Signed-off-by: Connor1996 <zbk602423539@gmail.com>

Signed-off-by: sre-bot <sre-bot@pingcap.com>

Signed-off-by: Little-Wallace <bupt2013211450@gmail.com>

Update rocksdb to include the following changes:
```
d9ac7463e 2019-10-29 yiwu@pingcap.com     Cherry-pick compile error fixes (#129)
8a63fcbfe 2019-10-29 yiwu@pingcap.com     Fix OnFlushCompleted fired before flush result write to MANIFEST (#5908) (#127)
```
Signed-off-by: Yi Wu <yiwu@pingcap.com>

Signed-off-by: Connor1996 <zbk602423539@gmail.com>

Signed-off-by: Connor1996 <zbk602423539@gmail.com>

Signed-off-by: Connor1996 <zbk602423539@gmail.com>