Change handling of EPSG/SRID to match standard

[bernardd]

PostGIS' ST_AsGeoJSON() function (http://www.postgis.net/docs/ST_AsGeoJSON.html) produces a CRS field with a colon between EPSG and the SRID integer, eg EPSG:4326. Googling around, this appears to be the standard way of doing things. The existing code expects no colon (EPSG4326). I've changed it to match what seems to be the standard.

The catch with this change is that anyone who's encoded a geom with the old code will not be able to decode with the new version. If you think that's likely to be an issue, it could be resolved by adding back in the old clause for get_srid/1 between the new version and the version that takes nil. I didn't do that in order to keep the code simple, but I have no problem with doing so.

[bryanjos]

@bernardd you are correct and it is a bug. To disrupt the least amount of people in the short term, could you add the function head that searches for the colon instead of replacing the existing one?

Something like:

defp get_srid(%{"type" => "name", "properties" => %{ "name" => "EPSG" <> srid } }) do
    {srid, _} = Integer.parse(srid)
    srid
end

defp get_srid(%{"type" => "name", "properties" => %{ "name" => "EPSG:" <> srid } }) do
    {srid, _} = Integer.parse(srid)
    srid
end

I think your change to add_crs should stay as is. That way any geoJSON created have the correct string

[bernardd]

Yep, can do. The clauses have to be the other way around or else the non-colon version will also catch inputs with the colon.

[bryanjos]

Looks good! Thanks!