Bunch of improvements, most importantly a default fallback behavior script which scrolls to the bottom of the page, and rearchitecting some stuff so that the behavior script can have some say on when it's finished with the page. Also some doc comments.
change magic first line of behavior js files to a commented-out json blob, which should include the fields 'url_regex' and 'request_idle_timeout_sec'; behavior.is_finished() incorporates the custom idle timeout into its check; also rename variables in behavior scripts with umbra/UMBRA_ prefix to sort of namespace them; and add "finished" logic to facebook and vimeo behaviors (flickr needs work to support it)
UmbraWorker.send_to_chrome() - central place to send message to chrome via websocket
clear UmbraWorker.self._behavior when finished with a page (after the first page, nothing was getting behaviors); bump hard timeout to 20 minutes
improve facebook behavior: when we expect a "close" button to appear, wait for it before moving on to other actions; and when we discover a missed click target above, scroll back up to click on it
"wasThrown" is necessarily always included in the result message from chrome for Runtime.evaluate
Merge pull request #22 from nlevitt/master

whole bunch of changes (already deployed on QA)