new optional argument will leave the carriage return and linefeed off the end of an NMEA sentence.
move addChecksum() to NMEA_build.cpp
We want to avoid using doubles where unnessesary since many embedded targets have only a single precision FPU or no FPU at all. Passing doubles is unavoidable with the printf family of functions, so use an explicit cast to silence the warning.
Rick Sellens
Owen Torres