Create pool implementation

Most connectors use some pool to handle the connections.
The main reason is that establishing a new connection with old databases wasn't very effective. That has changed and establishing a connection has always been performant in MariaDB.

Still...
creating a basic connection (no SSL, using the basic authentication method) is still a lot more consuming than reusing an existing connection with a simple query to reset connection state (with COM_RESET).

This would benefit to other connector based on C/C too