Rocksdict

What's Changed
* Update pyo3 to v0.18.0 by Congyuwang in https://github.com/Congyuwang/RocksDict/pull/39
* Add support for with statements by scientificworld in https://github.com/Congyuwang/RocksDict/pull/37

New Contributors
* scientificworld made their first contribution in https://github.com/Congyuwang/RocksDict/pull/37

**Full Changelog**: https://github.com/Congyuwang/RocksDict/compare/v0.3.5...v0.3.6

Rdict.destroy() now deletes rocksdict-config.json before calling DB::destroy(), also deleting the whole directory if no file is left.

New feature:

- Rdict(path) now automatically reads columnfamilies and their options from path.
- Use opt, cols = Options.load_latest(path) to read latest options from db path

Bug fix:
- automatically add "default" column when opening with `column_families`. Make compatible with v0.2.x releases