Update links to new version of application note AN0028
Add Config_GPS_param_search_engine_num and Q_GPS_param_search_engine_num input message classes, and GPS_param_search_engine_num output message class

Added in version 1.4.28 of AN0028 (April 16 2004).
Add bit 7 ('All SBAS PRN 120~138') to Config_SBAS and GNSS_SBAS classes

Added in version 1.4.29 of AN0028 (April 23 2014)
Move "PPSmode" out of NMEA0183 into SkyTraq and rename it to "TimingMode"

This enum is used by a proprietary NMEA-0183 sentence and a new binary message.
Add Config_1PPS_timing and Q_1PPS_timing input message classes, and GNSS_1PPS_timing output message class

Added in version 1.4.29 of AN0028 (April 23 2014)
Add Config_1PPS_freq_output and Q_1PPS_freq_output input message classes, and GNSS_1PPS_freq_output output message class

Added to version 1.4.30 of AN0028 (April 24 2014).
Add Config_GNSS_datum_index and Q_GNSS_datum_index input message classes, and GNSS_datum_index output message class

Added in version 1.4.31 of AN0028 (May 15 2014)
Add some constructor docs for new input message classes
Fix all of the class documentation so that Doxygen knows that the first line is a brief