Use AFMotion instead of BubbleWrap for HTTP (redux)

Hello,

I came across @killion's PR at https://github.com/tkadauke/motion-resource/pull/23 and took a stab at incorporating @tkadauke's feedback from that PR into this one (this branch is actually branched off of killion's from #23).

There's a potentially big caveat to this PR, however. It seems that the rubygems version of afmotion breaks the motion-support callbacks functionality (or at the very least breaks the specs - I haven't tested the callbacks in the wild yet). Hence the added afmotion from github in the Gemfile. For the life of me, I can't figure out what is going on there, since the last commit in afmotion coincides with the bump of gem version as well as the release on github and rubygems. The gemspec doesn't provide for using a github repo, so I'm not exactly sure how to proceed there. That seems like a maintainer-level consideration, so @tkadauke if you know how you want to approach that, please let me know.

Other than that, there's a lot of trailing whitespace cleanup that is incidental to this PR. I have an editor plugin to kill that wherever I find it. This PR was my first experience with motion-resource, so please let me know if there's anything awry in it or if anything needs changing.

Cheers,

Mark