Allow exporting of hook implementations

Seems to me that once you've written a hook implementation using hooker, one might want make the implementation a little more permanent than just a row in the database.

The excellent ctools module provides an easy way for modules to provide exportables, this would provide a super easy way to export hooks from hooker into code. This would have many advantages and allow users to store the hooks in a VCS or even share them. I think there is potential for an entire ecosystem of people sharing useful implementations of hooks.

I've noticed that hooker depends on bad judgement, so this feature is clearly a shoe-in for inclusion in the next release.