Add error handling to HardwareSerial

Check for USART receive error flags and call serialError{|1|2|3} at serialEventRun(). Currently the error flags are not stored in the HardwareSerial class and are cleared after every call.
Revert "Add framing error (frame error) handling to HardwareSerial"

This reverts commit fba6adea9812ec268c5a65efb7a720b02e118006.
Merge branch 'serialError'