Logging improvements proposal

[João Reis]

Hi,

I just opened a PR to introduce some significant logging changes and I'd like to ask other community members for their feedback on this proposal. Hopefully this proposal will not change the behavior of any existing applications that leverage the current logger interface that gocql offers but ideally a new logger interface that is potentially added now would eventually replace the existing one (maybe in a version 2 release of gocql?) so any feedback that people might have on this PR would be super useful.

Thanks!

João Reis