Major changes to inetegrate LIN UART into module.

Major changes made to integrate LIN UART module into HardwareSerial.
Unfortunately doesn't compile - too many/little #ifdefs or brackets
somewhere.
Final edits to add LIN UART support.

Edited HardwareSerial.* to complete LIN UART support. Files now
compile without error in IDE. Don't know if it actually works though!