Moved HardwareSerial::flush to 1.0.0 method.  Added hardware TX fifo
Revert "Moved HardwareSerial::flush to 1.0.0 method.  Added hardware TX fifo"

This reverts commit f56e18ce69afc1f4598831b948e7a9a50ea1da83.
Moved HardwareSerial::flush() to purge()
Implemented 1.0.x HardwareSerial.flush()
Enabled full use of TX fifo in Hardware Serial
Merge pull request #353 from majenkotech/master

Implemented Arduino 1.0.x flush() in HardwareSerial