Update LICENSE file
Unknown configuration section exception clarified
Not used constants removed from binstub
Removed references of Behat from Testwork
Clearer verbosity constant names used
If Behat couldn't generate snippets - it tells user about that

Before this if context didn't implement *AcceptingContext interface
snippet generators were silently failing, giving user no feedback except
bunch of undefined steps. From now on, if Behat can't generate snippets
for some steps of specific test suite - it will explicitly tell user about
that.