The first occurs when starting a read transaction from a slave that doesn't respond. The code would wait until the SB (slave on bus) bit is set in the INTFLAGS register, but when a nack occurs that never happens so we're stuck in an infinite loop. The fix is to also look for the MB flag to be set. If it is, issue a stop condition and return.

The second happens when a bus error (ie, an illegal stop condition) occurs while sending data as a master. In that case we are waiting for the MB (master on bus) flag to be set. When a bus error occurs that never happens, so again we end up in an infinite loop. The fix here is to also look for the BUSERR flag to be set. If it is, return an error condition.

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).

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

 WIRE class finished. SERCOM class completed. Few correction in HardwareSerial and SERCOMUsart after compilation

Add SPI functions into SERCOM class and create SPI class