Impl display compaction reason (#244)

* impl display for compaction_reason
Signed-off-by: zhangjinpeng1987 <zhangjinpeng@pingcap.com>

* format code
Signed-off-by: zhangjinpeng1987 <zhangjinpeng@pingcap.com>

librocksdb_sys/src/lib.rs

@@ -20,6 +20,7 @@ extern crate tempdir;
 
 use libc::{c_char, c_double, c_int, c_uchar, c_void, size_t, uint32_t, uint64_t, uint8_t};
 use std::ffi::CStr;
+use std::fmt;
 
 pub enum Options {}
 pub enum ColumnFamilyDescriptor {}
@@ -202,6 +203,12 @@ pub enum CompactionReason {
     NumOfReasons,
 }
 
+impl fmt::Display for CompactionReason {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{:?}", self)
+    }
+}
+
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 #[repr(C)]
 pub enum DBInfoLogLevel {