Add VHW sentence parser

[ekuinox]

#54 Implements parser for VHW sentence.

Different definitions seem to exist, but for the time being, the implementation follows gpsd.

[GLOBALSAT] describes a different format in which the first three fields are water-temperature measurements. It’s not clear which is correct.

From https://gpsd.gitlab.io/gpsd/NMEA.html#_vhw_water_speed_and_heading

[codecov]

Codecov Report

Patch coverage: 95.83% and project coverage change: +0.33 🎉

Comparison is base (750e0a9) 80.39% compared to head (c0139e5) 80.72%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #84      +/-   ##
==========================================
+ Coverage   80.39%   80.72%   +0.33%     
==========================================
  Files          29       30       +1     
  Lines        1076     1100      +24     
==========================================
+ Hits          865      888      +23     
- Misses        211      212       +1     

Impacted Files	Coverage Δ
src/lib.rs	0.00% <ø> (ø)
src/parser.rs	77.30% <0.00%> (-0.30%)	⬇️
src/sentences/mod.rs	0.00% <ø> (ø)
src/parse.rs	71.95% <100.00%> (+0.70%)	⬆️
src/sentences/vhw.rs	100.00% <100.00%> (ø)

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[elpiel]

Thank you for your PR!