Init AFSK::m_isSending to false
Queue::enqueue now returns whether successful or not

Will return true if the character was successfully added to the queue
and false if the queue was already full.
Add FakeGPS module

This module simulates a GPS device by sending a fixed set of NMEA
sentences out from a UART.
Update GPS module

Now has hadLinesToDecode() method so that the main thread can know
whether it should call decodeAvailableLines() to process any queued up
NMEA sentences.

I also fixed a few other issues in the GPS module:
* Drop any '\0' characters received from serial port so that they don't
  get treated as sentence terminators.
* Don't increment m_lineCount if failed to enqueue the '\0' sentence
  terminator.
* decodeAvailableLines() now loops through characters until the
  decode() method returns true, indicating that the end of a sentence
  has been encountered.  decodeAvailableLines() now has the code to
  check if it has received enough valid sentences to update the pData
  structure.

NOTE: I have updated config.h in this commit to have a clean set of
      initial values, some of which make it not work on my setup
      because I have no real GPS hardware.  Enabling the FakeGPS
      module does make it work but others probably don't want that
      turned on by default.