Enabled testing on HHVM
Marked HHVM as officially supported
Added the external code coverage for Scrutinizer
Added the scrutinizer badges

[ci skip]
Changed some magic methods to the documented ones

This makes the static analysis tools happier.
Changed the phpdoc to use inheritdoc

Refs Behat/Mink#425
Fixed CS
Reverted a bad change of magic method

The WebDriver Session documents getUrl() rather than url() to access the
current url, but there is actually a getURL() in a parent class.
Removed unused argument in the protected helper method
Merge pull request #109 from stof/clean_unused_code

Removed unused argument in the protected helper method