Image Size Parameter

[PanisSupraOmnia]

Summary

Closes #131.

This PR adds the ability to specify a size for the image returned for a variety of CDN endpoints. I also improved the Overcommit configuration since I happened to run into an issue with it while committing the changes for this PR; I realize these are unrelated changes so I can split them to a separate PR if you'd like.

---

Added

• The size of image can now be requested for CDN-served images.

Fixed

• Made Overcommit invoke RuboCop via Bundler, to ensure we are using the currently specified version.
• Re-enabled Overcommit's AuthorName check because the original behavior of the check that prompted it to be disabled has been changed upstream; first and last name are no longer required, anything of non-zero length is sufficient.

[swarley]

I'm fine with size being a kwarg here, but for consistency's sake I wonder if we should keep it as an optional positional. I'd like some input