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
 - [ ] add documentation / docstrings
 - [ ] figure out how to display added/removed spaces



+1 for separate function, but do not put it in `github.py`, leave that for github stuff. make a `review` module in the easybuild.framework.easyconfig` namespace