B+ Revision check & Pins

This was my attempt at creating a PR for issue #8. I was not sure what to do with the hackablePins array as I'm not entirely sure what the purpose of that array is. Hope this helps get things up to date for the B+. Changes seem to be working okay with mine when it comes to reading pins, have no started messing with blinking pins.
could you please elaborate a little on that?

This little `& 0xf` was introduced by @basbloemsaat, and he wrote a [unit test](https://github.com/ronanguilloux/php-gpio/blob/master/tests/PhpGpio/Tests/PiTest.php) for that method. Unfortunately, Travis fails at unit-testing Raspberry Pi (:trollface:) so you/we have to run such phpunit tests locally & verify that they all remain green. Grabbing a new Raspi B+ is part of my project lists, but I have no possibility to verify this is ok, so can you check these phpunit for us & tell us a bit more ?