Support LevelDB

**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

