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

```python
chars.insert(0, cmap.get(line[0],'')
```