Split/reorganize repo into separate categories

@tpm yesterday suggested that it would be good to reorganize the repo into various categories, like audio, video, net, misc, etc.

That way you would have the option to build everything at the top-level, only the category inside that directory and only a single plugin from inside the directory.

Advantage would be that we wouldn't have to build all 100000 dependencies.

@tpm were there other things you thought why this would be a good idea?