Enumerate missing components wrt the latest RocksDB version

[eladn]

Maintain a list of missing components wrt the latest RocksDB version. This will help focusing the contributors' effort, and thus can boost up the development of this fork to eventually become and kept up-to-date.

Side note: I must mention that maintaining this project is a great and important initiative, as RocksDB is a highly functional asset (which is itself still under frequent development and maintenance), and should be accessible for the python's community.