Commented and changed code in pwm_set_channel_frequency().
Removed doxygen documentation from pwm.c
Change the way comment were written for pwm_clk_setting.
Corercted doxygen formating
Corrected doxygen format in sevral files.
Removed versioning in doxygen comment from bitwise_operations.c
Changed comment in pio.h
Turned bitwise_operation.c into an API and commented on the code.
Changes based on feedback from Ulrik on mapping
Merge remote-tracking branch 'origin/arduino_pin_mapping' into integration