Merge pull request #18 from proan/arduino

Rename of "internal" to "built-in" to work around Arduino's #defines
Added byte that tells arduino to use gpio write or read
Changed the data type of read to a reference to get the read value
Fixed built in device type in gpio read
Merge pull request #19 from sebEg/gpio-develop

We should change the rest of the read() functions to also do pass-by-reference.
Added byte that tells arduino to set pwm signal
Fixed function convertDutyCycle
Merge pull request #20 from sebEg/develop-pwm

PWM fix
Update arduino_interface to work with BUILT_IN devices.
Updated to work with BUILT_IN.
Updated gpio_driver to use BUILT_IN.