Add query method to avoid method_missing for most SQL DB connections

[rubencaro]

I've come adding this for performance, as almost every use I make of this pool is for MySQL connections, and almost every call I made on them is to query.

Maybe you could merge it as it does not really bother much the rest of the code. Maybe not. Your choice!

Thanks anyway.

[djanowski]

If you have a specialized pool and don't want to hit method_missing and don't want to use ConnectionPool#with you should implement your own object. For instance: https://github.com/djanowski/redic-pool/blob/master/lib/redic/pool.rb

[rubencaro]

You are absolutely right. Thanks!