Improve article attribution heuristic

Make the attribution algorithm trace through the history
across file rename operations, but do not consider such operations as an
indication of contribution.

The compiled output is a single line of JSON, making it a bit tough to inspect.
Here's what I did to try it out:

    $ git checkout -b tmp master
    $ grunt
    $ git add -f dist
    $ git commit -m "Current build"
    $ git pull git@github.com:jugglinmike/learn.jquery.com.git follow-moves
    $ grunt
    $ git diff --word-diff --word-diff-regex="[^,\{]"

Basically, it adds contributors who created/edited articles prior to 0fb17c3b126823445015d373c738f5930af529d3 (including yours truly) and removes contributors whose only interaction with an article was to move it (i.e. @rdworth in  07113756905d4edead15191650fcf076ae354666 and 7b49f826153fc27f510322eb56f23f3b4743be29).