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



I haven't looked at the rest of the code, so maybe this is redundant:
wouldn't `not ==1` do the job better, to catch the empty case?