Bug fix for bus intialization

Previously the library would not re-initialize hardware if you called begin. That wasn't a good idea as it would lock up the CAN hardware if you connect to the wrong bus speed. Now you can call begin any time you need to in order to re-initialize the hardware.

Object oriented support, bug fixes

The library now supports doing direct callbacks to objects instead of requiring non-OOP code for the callbacks. Also, several bugs have been squashed.

First stable version of canbus library

This is the first release of the stable version of the library. Commits after this point can (and did) break existing code that relies on this library.