Revert "Removed built-in generator registration"

This reverts commit 5ab5b483a3c2ad2f39a2ff4e2c285740ecd265e9.

It caused symlinked generators not to be registered.
Merge pull request #57 from stephenplusplus/master

Show outdated generators in `yoyo`
Use `files` property in package.json
Update dependencies
Bump version
(yoyo) explanation messages.
(yoyo) don't respawn, just run env.lookup()
(yoyo) fix pkg.namespace removal!