Better logging and output

[BPHarris]

It may be beneficial to go through all existing logging, output, error messages, etc and ensure that the are all sufficiently distinct and informative. While doing so two additional goals may be accomplished:

1. add additional output/errors which are themselves distinct and informative when-and-where rattr will benefit from this;
2. group each rattr error message into a category (and decide on the categories in the process);

after completing this it will be possible to begin the process of documenting each error along with an example and fix in the wiki pages.

This is a prerequisite to #20