Introduce connection pooler

Yes and no. The predefined UNIX endpoint used by the connection pooler is the one that is harcoded in __init__(). The class user might not want use anything else than the predefined path, if no he can change it at instantiation. Nevertheless we don't have a configuration file other than archipelago.conf which at the moment is not used for such kind of settings. Even if we use this configuration file there is always the option to not set, as you can easily see, the specific setting and use the default one defined at compilation time (/var/run/archipelago/poold.socket).
Do you believe that we are going to have a problem with this approach?