Issue 27

I took the changes from @asgrim in his PR #27, made them working also with hhvm and reduced the amount of tests.

I also removed an alias to a not existing branch from the composer.json and tests for PHP 5.3.3 from .tavis.yml because it throws this error `*** glibc detected *** php: corrupted double-linked list: 0x0000000009043770 ***` after creating the code coverage.