Normalize underscore and camelCase usage in filenames to hyphens, except where significant (ie, Dockerfile, *_test.go, etc)

We've discussed (and decided to) standardize on using hyphens in filenames before, but never bothered to update many of the existing filenames in the repo to reflect that decision.

The list of files needing renaming was generated with the following command (using GNU Find, probably won't work with OS X's find as written, but gfind from homebrew should work swell, or adapting the GNU-specific options to their "proper" names would probably work also):

  find -not \( \( -path ./.git -or -path ./docs -or -path ./vendor \) -prune \) -and \( -name '*_*' -or -name '*[A-Z]*' \)

Then, it was just a matter of looking through a few files in hack/infrastructure to make sure the files renamed were being referenced by their new names.

I decided not to touch the docs, since I didn't want to go digging in RTD/RST documentation, and that would be updating user-facing URLs, so we'd want some kind of transition plan for that (if that's even possible there).  ie, too many issues there I wouldn't be able to help solve. :)