Adding random port and slight delay.

1. Phantomjs now starts up on a random port, between 40,000 and 60,000. Allows chapturejs to run in parallel.

2. render() is now called with a 250ms timeout, to give javascript a chance to render before we capture.

It might be nice to make the timeout configurable via the command line, and/or pass in the port instead of randomly picking one.