Add logging facilities

[tmadlener]

Currently podio logs directly to stdout or stderr in a limited number of places. It would be nice if these messages could be picked up (and silenced depending on level) by downstream consumers.

This will require at least some logging facilities that make it possible to do so. One possible approach is to pass a logger object to all functions or object that need to do logging (defaulted to some default logger that preserves current behavior).