Summary:
I made another rust binding. 👻
* Use C++ API (instead of C API)
* Try to follow [Rust Guidelines](https://aturon.github.io/README.html)
* Working in progress (the APIs are not stable yet)
Closes https://github.com/facebook/rocksdb/pull/2438
Differential Revision: D5690612
Pulled By: siying
fbshipit-source-id: 11d3956c33b5e5366555afbf3786b782be3046e7