Add pwm support for pin_t;
Add analog_value= method to Pin class;
Move constants to beaglebone.h
Fix -Woverflow warning in constants definition;
Fix compiler warnings;
Update version to 0.0.3;
Update require location to bonekit.so shared object file;
Major refactoring for 0.0.3:
* Improved beaglebone pin constants;
* Add Pin pwm support;
* Update spec;
* Update test;
* Add analog/fading.rb example;
Renamed unit test;
Update README.md with analog_value= examples;