Add ability to read a stream in a ranged loop

[Chris--A]

By adding in an iterator for stream reading, the two step process of checking for available data, and reading the character can become a single operation.

StreamEx s = Serial;

for( char c : s ){
  //got char 'c'
}

This would be the equivalent to:

  int current;
  while( (current = Serial.read()) != -1 ){
    //do something with current.
  }