New validation options

• Because the NMEA checksum is not very good at error detection, extra validation test can be performed:
  • Character validation simply checks whether a particular character is valid for a field. For example, integer fields can only contain digits 0 to 9.
  • Field validation checks whether a parsed field value is in an acceptable range. For example, latitude degrees must be between -90 and +90.
• The options are in NMEAGPS_cfg.h
• This increases the program size (extra code) and the execution time (extra tests).
• This version validates only the N/S field of a location. Future releases will contain validation of all fields.