Update example
Allow custom logging in zetta and option to silent log output. Also adds info, warn, error log levels.
Updated tests to silence all zetta instances.
Added basic tests for custom logging interface
Merge pull request #113 from zettajs/custom-logging

Custom logging
Added error handling in the callbacks for _cleanUpPeers, and _initPeers.
Merge branch 'peer-delete' of https://github.com/zettajs/zetta into peer-delete