Offer OpenStreetMap option

[relrod]

@kg4sgp and I discussed this at length and I think this is a good thing to have as an option. A few comments:

• There's a lot of purescript machinery right now that I wrote for working Google Maps. I don't want to just nuke all of that (ideally, I'd like to split it out into its own library for people to use).
• We'd have to write similar machinery for some OSM map viewer such as Leaflet. I've worked with Leaflet before and I like it quite a bit, and I'm more than happy to write the FFI machinery.
• I'd like to leave GMaps as a supported option. I don't care if it's a compile-time option or a runtime option, but I'd like to leave the option around, in case people want it. I am hoping that, once we use this setup a few times successfully, others might become interested in using it as well, and they might want GMaps (OSM often lacks things, etc. The main advantage for us, though, is that it's available offline.)
  • Speaking of offline, we need to figure out how to do offline tiling. By "offline" I mean that someone in the chasecar runs both mapview and mapview-psc and only needs a radio, no internet connection. This means that something in mapview or mapview-psc can serve tiles. When @kg4sgp and I discussed this some, we found mod_tile, but this would tie us to Apache which is less than ideal -- we already incur a large penalty in terms of the number of things we depend on (haskell, purescript (thus nodejs), minimodem, etc.).

[kg4sgp]

Indeed, and to add a few comments... I think it would be wonderful to provide an OSM option. What OSM doesn't have is good addressing data (useful in geocoding) however this is not a problem for the objective we're trying to solve. It does have good and accurate street coverage though, and is available off line, which is exactly the problem we are trying to solve.