HardwareSerial modifications

Added the possibility to configure the hardware serial port for 9 bit comunication and added an event (processed like SerialEvent) for a txfinished interrupt (usefull if you're using the serial port with a rs485 transceiver to drive RE/DE line).
I've tested the modifications with an arduino mega2560 and a pic microcontroller as a receiver with Serial1.

for use the txFinished event you should have a function like this:

void transmissionFinishedEvent1(){
   doSomething...
}