Prettify logging

[twalker]

This improves logging by:

• Prefixing log entries to distinguish mocker entries from other output.

• Adds info, warn, and error colored levels to logger.

  

• More consistently log information for mock responses using middleware.

  

This is an implementation for issue #92

[gstroup]

Looks great! Thanks a lot.

[gstroup]

Addresses issue #92