allow overriding of sentence structure defines

[Kriechi]

This is needed for NMEA-like protocols that add extensions with longer-than-expected sentences, or new longer type words. Users that need to, can now define their own limits or use the default defines.

For example, Quectel uses vendor-specific type words longer than the usual 5 characters: https://github.com/quectel-open-source/GNSSTool/blob/42987f2ac4026e32c7839691a561f86ff655b737/QGNSS/DataParser/nmea_parser.cpp#L432

[jacketizer]

Looks good! I will take a closer look later.

[Kriechi]

@jacketizer any chance to get a review on this? Thanks!