Support LevelDB

[chungquantin]

Is your feature request related to a problem? Please describe.
LevelDB is built on top of RocksDB, it's great to have this database in the list too

Describe the solution you'd like
Can use this repo as reference: https://github.com/skade/leveldb
However it is not a very great repo

Describe alternatives you've considered
FFI to C++ leveldb