Add build step to fetch mime.types from Apache and build types.json

[broofa]

Finally getting around to addressing #61. ~~~This also uses request to fetch Apache's mime.types file from the source URL, rather than keeping a possibly out-of-date version in this repo, which has caused confusion for people wanting to add new types. (Of course, I'm sure those same people will end up editing types.json, but that's an issue for another day.)~~~
Edit: Using mime-db instead, since they handle all the nastiness around aggregating mime resources and community extensions. Makes code a lot simpler. So, really, at this point the only thing node-mime will offer over something like mime-types is that the types.json file it generates is a little more compact, and it allows for project-specific customization via define().

[braddunbar]

This looks rather nice to me! 👍 I'd love to use mime via browserify.

[broofa]

Reworked code to use mime-db as canonical source of mime types. (I'll be working with mime-db team to insure node.types extensions are incorporated into mime-db.)