Update Readme

- add darinkes to contributors
- add minimal section for style guide
update TODO list for graveio
Merge pull request #22 from darinkes/like_dislike

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Fix broken tests intorduced with devise
create diff only if content changed

Diffs just make sense if there is actually a diff.
So just update the post if content is unchanged, else
create a new version of the post for diffing.