This fix lock-ups on UART errors (for example when disconnecting
and reconnecting RX/TX wires or if the method Serial.begin is
called while another device is already transmitting).

Fixes #4

It seems that

   #include <stdint.h>

is able to undef "min" and "max" previously defined. With this
commit we make sure that they are defined as last.

Fix #10

as in the other Arduino cores

Signed-off-by: Thibaut VIARD <thibaut.viard@atmel.com>

Signed-off-by: Thibaut VIARD <thibaut.viard@atmel.com>

Signed-off-by: Thibaut VIARD <thibaut.viard@atmel.com>

Interrupt based implementation that works on every pin.

- Renamed Tone.cpp.disabled to Tone.cpp
- Removed commented legacy AVR code from Tone.cpp

This reverts commit bc7115b104428f9bea4fdfa1b6af245085f6f542.