This patch remove remoteDebuggingPort option. Instead, browser
is launched with '--remote-debugging-port=0' flag, letting browser
to pick any port. The puppeteer reads the port number from the
browser's stderr stream.
This change cuts average browser start time from 300ms to 250ms
on my machine. This happens since puppeteer doesn't have to probe
network once every 100ms, waiting for the remote debugging server to
instantiate.
Fixes#21.
This patch introduces check_availability.js utility which looks for
available chromium binaries for different revisions and platforms.
This patch also re-factors the chromium downloader scripts so that
it can operate different platforms.
