Clean up browser creation & destruction

[jfinkhaeuser]

• Check defaults when using browser.create. It currently uses configuration defaults, but IMHO should use the same configuration as when using browser directly, with the ability to override.
• Ensure browsers created by browser.create also get destroyed.

[jfinkhaeuser]

Mostly fixed in (upcoming) 0.7 release. Review of interest.

[barzilay]

Fixed in ll 1.0. Closing after end is not possible because connection to the browser is already lost. Closing happens just before that happens.

[sjieg]

# Making sure all browsers are gracefully closed when the exit event is triggered.
at_exit { LapisLazuli::Browser::close_all 'exit event trigger' }

this piece of code ensured a positive destruction.