Added a better support for serial communication

This commit allows to use the UART just like another bus.
The serial communication is initiated with *ser = initSerial('port', baudrate, timeout)*
A command will be automatically sent to the LPC to configure pin 0 and 1 (PIO0_18 and PIO0_19) to their secondary functions.

It's better to test this feature with a ftdi chip and a PC. It's also possible to short-wire pin0 and 1 to create a loopback, but in this case, the LPC won't works (stuck in interrupt routine…)