fix: #32 display diffs between commits

So I know this is a duplicate to #332 but I had a need for this future for myself recently and worked on it.  I see that @Fabbi finished but since I started it I figure I would finish it...  :P

Known problems:
* doesn't handle images yet.  will be updating that later
* Haven't done edge case testings such as merge conflicts, and etc but did general round about testing and will be adding test cases later.