Adding network.wait_for_idle options

[ron-shinall]

@excid3 Thanks for this gem! I'm converting our application to use this, however, I ran into an issue that requires page.go_to(url) to call page.network.wait_for_idle to allow in-page JavaScript processing to finish. As such, I made a few changes and would appreciate your review, feedback, and consideration.

This PR:

• Moves page.network.wait_for_idle outside the browser.create_page if...else block so that both cases can make use of it
• Adds wait_for_idle_options named parameter to render_pdf to allow setting all of the available network.wait_for_idle options
• Adds ensure with page.close to clean up network connections
• Updates the Readme
• And, since I was there, simplifies the authorize hash to **authorize in browser.create_page