Use Stream instead of *Serial/TwoWire

for newer arduinos,
- HardwareSerial
- NewSoftSerial
- TwoWire
- Serial_ (USB CDC)
are all subclass of the Stream abstract class.

and this way we automagically supports all transfer method which is
derivered from Stream.
Merge pull request #4 from Palatis/master

Use Stream instead of *Serial/TwoWire; major props to Palatis