NMEAGPS reduced

* Disconnected from IOStream::Device and Event::Handler (removes need
for 'volatile').
* Added example programs to show stand-alone, non-interrupt, and
interrupt+event techniques.
* Enable conditional compilation of NMEA sentences.
* Added 'double' accessors to retain precision lost by a single 'float'
conversion.
* Added 'run' method to ublox to accommodate methods that block while
waiting for a protocol ACK (e.g., send and poll, not xxx_request).
* Slight distinction made in /rxEnd/ for received messages that should
be visible (aka public).  ACK/NAKs are private, and blocking method
/poll/ implies that the message is privately handled.