Update docs.
Add download_url_resolver, URL detection.
Use substrings rather than regexes for URL detection.
Add cheerio.
Add URL resolving for Mediafire.

Also included is a fixture for Mediafire pages.
Listen for DOMContentLoaded in page_loader.js

The DOMContentLoaded event happens a few *seconds* before the document.ready
event, making things quite a bit faster.

In tests, this makes things take 8-9 seconds rather than 15-16 seconds. Still
very slow, but it's progress.
Add resolving for Dropbox links.
Add Box URL resolving.
Add request, nock.
Stop using chdir.

Chdir doesn't work with promises (changing directory in Node is a stateful and
syncronous action and chdir can't do anything about that). For now, the solution
is to simply prepend commits intended for a particular directory are prepended
with a `cd directory ;`. Ugly, but it works consistently.
ChildProcess#exec returns stdout, stderr in an array.

I misunderstood how bluebird's promisify works with multi-argument-returning
functions.
Add support for direct Mediafire URLs.