Update talker.py - adding RSD

[mnissov]

Adding radar system data (RSD) message type, according to https://gpsd.gitlab.io/gpsd/NMEA.html.

[coveralls]

Coverage increased (+0.006%) to 98.083% when pulling 4d646fa on mnissov:master into 4527cf4 on Knio:master.

[Knio]

Thanks! Can you provide any example sentences to use in a unit test?

[mnissov]

Of course, I'll just write them here unless you want them somewhere else?

Some examples I've found online
$RARSD,,,,,,,,,0.000,000.2,0.125,N,N*50
$RARSD,0.883,099.3,0.200,047.6,,,,,0.145,245.2,0.1 25,N,N*74

[dimidagd]

Can we merge by now? thanks