Implement Logger interface

[yiwu-arbug]

Implement the Logger interface to allow writing a Logger object in rust and pass it to rocksdb.

The Logger interface: https://github.com/facebook/rocksdb/blob/master/include/rocksdb/env.h#L972

You can look at src/slice_transform.rs for an example to see how to turn interface in c++ into a rust one.

[yiwu-arbug]

cc @glommy-left-hand