libarduino: change the structure of the library to separate into different for files for each peripheral.
Instead of having everything in a single libarduino.c/.h files, it comes with:
- libarduino.h: global switches (ENABLE_xxx) + peripheral include (user API)
- adc.c/.h: API for the ADC
- pwm.c/.h: API for both the PWM & PWMSERVO
- ir.c/.h: API for the infrared interface
- gpio.c/.h: pin configuration API
- uart.c/.h: UART0 interface API.

Code examples are provided in the example/ directory.
The default example (main.c) is actually the adc/uart example.