Add warning when building without defeatureify.
Merge pull request #99 from rjackson/make_dist_warn_without_defeatureify

Add warning when building without defeatureify.
Use `defeatureify` from local node_modules.

Also, moves `yuidocjs` into node_modules, and resolves a long standing
issue with using `which` (doesn't work on Windows).

Resolves #97.
Resolves #54.