Update examples;
Add Spec for Pin Class;
Add unit test for Pin Class;
Refactoring:
* ext/gpio;
* ext/pin;
* rbinit;
Remove unused files from ext/;
Fix issues in gpio_read;
Refactoring of c extension:
* Move class wrapper to class_*.c;
* Update rbinit;
Add Pin class documentation;
Review spec;
Review unit test for Pin class;