CassSession missing functions

[Lorak-mmk]

Some functions are still missing

• [x] cass_session_connect_keyspace
• [x] cass_session_connect_keyspace_n
• [x] cass_session_close
• [x] cass_session_prepare_from_existing
• [ ] cass_session_get_metrics
• [ ] cass_session_get_speculative_execution_metrics
• [ ] cass_session_get_client_id

First 3 are the most important (and probably are supported by rust driver). prepare_from_existing might be problematic - Rust driver doesn't support it (and I think they are right to, it's a stupid API imho), so we should think if this can be implemented in the wrapper. Last one - easy if Rust supports. metrics - I don't think Rust supports it (but it's great if they do), what should we do about them?

[roydahan]

The missing ones are part of the plan. Closing in favor of dedicated issues.