Feature/add review pr option

use `./eb --review-pr 1017 -D | less -R` to try this out.
TODO:
 - [ ] Compare with other files found in the same PR
 - [ ] add legend on top
 - [x] add documentation / docstrings
 - [x] figure out how to display added/removed spaces



it may make for a bit longer code later on, but wouldn't you like a dict for generality? such as:
https://github.com/dhcmrlchtdj/toolkit/blob/master/snippet/python/clogger.py
http://stackoverflow.com/questions/17771287/python-octal-escape-character-033-from-a-dictionary-value-translates-in-a-prin