Add package.json and .gitignore
Make world.json compilation an npm prepublish step

Instead of doing this manually, make it part of npm prepublish. This will
compile world.json from the Natural Earth archive whenever this project is
installed.

As part of this, compile_world_json now uses the local topojson instead of
assuming that there is a global one installed.
Add a simple HTTP file server

This simple server will serve up the various files we need for the map.