Adding mmsi_transit values

Positional messages now include an mmsi_transit value, which connects continuous sequences of movement by individual vessels. See src/aisutil/transit.d for a spec.

Bugfix release

Resolves crash while decoding larger MCA data files

Update with improved output fields

Now handling key AIS sentinel values as optional/null fields, and including fairly detailed documentation for all output data fields

Update with MCA data reading

64 bit Windows build of the GUI, now including UK Maritime and Coastguard Authority data file format support

First release

Windows binary of the GUI included.
Let us know if it would help to provide Linux builds too, or a Windows build of the command line program.