Run benchmark automatically, support POSTing results.

This is some initial work to integrate this with the mozbench framework I'm working on.

I'd like to be able to set Massive to run automatically, so I've added an autoRun url parameter.

I've also changed the sendToURL to be postToURL and added support for a json structure which includes the subresults as well as the final score. Please let me know if it would be better to keep both.