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



watch out, if it comes from stackoverflow, this will turn the whole code into CC-BY-SA, sharealike :-P
http://creativecommons.org/licenses/by-sa/3.0/
Being more serious on it, adding these in a pool of "external" functions, would be the pristine way to go about it.