Fix compilation on ARM for Rust >= 1.6

More idiomatic iterators?

Change iterator to take handle

This changes the DBIterator interface to match the convention of taking
a handle over a string as per the other column-family-aware apis.

Use more regular semver suggestion

This is the same as using ^, which is a bit nicer than ~ imho, and is the default for a reason :)

nuke db result

Fix all warnings

basic cf support