GPS support

It would be good to have working GPS support. We need GPSd and some kind of user application for that.

a) gpsd is easy:

stty 9600 < /dev/ttymxc2 sudo gpsd /dev/ttymxc2

(I don't have good enough reception to actually have a fix indoors, so not completely tested).

b) GUI application would be good. Default possibility is foxtrotgps. It works okay with remote X, but has bad problems rendering on internal screen; probably related to gtk2.

Fortunately, osmgpsmap has bindings for Rust and is easy to use: example is:

https://gitlab.com/tui/tui/blob/master/acaptain/src/maptest.rs

(I have adaptation that works on l5, not yet in tree)