Added basic Ping driver class.  Have output pwm working.  Input capture not working yet.
Have input capture working.  No time output yet.  Still need to be cleaned up.
Update ping driver with pulse duration.  Had to make ISR file a .cpp file to include PingSensor.
Finished cleaning up sonar sensor code.
Merged Garrett's code from 'messed_up_branch'.  Renamed files for consistency.