This PR adds utility functions that import/export landmap files to .miz
polygons. In addition to the unit test, this PR has been tested by
writing the Caucuses & Syria landmaps to a .miz file, loading the
generated .miz file back in and checking that the loaded landmap object
is identical to the original files.
Holes in the inclusion zone are defined by exclusion zones, not by holes
in the inclusion zone. Add a cached property for the inclusion zone that
is not also sea or exclusion zone and use that boundary instead.
Converts the landmap to use MultiPolygon instead of a collection of
polygons, since Shapely has explicit support for this.
Because we've done that, we can use a single projection from a line
instead of brute forcing the extent of the front line.
This makes turn processing ~66% faster (3 seconds to 1.8).
There are probably other places this should be used.
