Check pr commits

[nicolasgras]

This pull request resolves #236 (Add checks for commits in pull requests) A new feature has been defined to check if PR's commit list contains any merge or fixup commit and check run are created in PR to show results.

• If any merge commit if found in PR, then a check run is in FAILURE in PR and user can see which commits are involved. Otherwise, check run for merge commit analysis is in SUCCESS.
• If any fixup commit if found in PR, then a check run is in FAILURE in PR and user can see which commits are involved. Otherwise, check run for fixup commit analysis is in SUCCESS.

[gsmet]

I rebased to remove the merge commits. Believe it or not, we don't want them ;).

I also added a commit with some minor editorialization and dropped the Edited event as we don't want to run the checks just because the description has changed. We might tweak that later if we add more rules.

[gsmet]

Thanks, nice work!

[gsmet]

I just deployed the new version.

[nicolasgras]

My pleasure. Thanks for the review and the merge. :)