Some European River Information System function identifiers are not handled

[pyrog]

The following AIS_DAC_200_RIS FI are not decoded by libais:

FI	FI Group	Name of International Function Message
21	VTS	ETA at lock/bridge/terminal
22	VTS	RTA at lock/bridge/terminal

See:

• Vessel Tracking and Tracing Standard for Inland Navigation 2.4.4.1 Allocation of Function Identifiers (FI) within the Inland AIS branch
• Technical Clarifications on Vessel Tracking and Tracing Standard for Inland Navigation, Edition 1.2

[schwehr]

Please attach some sample NMEA with these messages and I will try to add these messages.

[pyrog]

I don't have any NMEA samples but I tried to code this. Could you comment my PR #165 please ?

(Sorry, code untested yet)

[pyrog]

Ooops ! DAC 200 FI 21 and 22 are used in Binary Addressed Message (AIS message type 6),
not in Binary Broadcast Message (AIS message type 8)

[schwehr]

I added some initial comments on https://github.com/schwehr/libais/pull/165