Need to create theme function for hook list

The hook list right now looks quite nasty, all in one big column. So I'd like to do two things:

1. Clean up the presentation here... I'm thinking putting each group into a collapsible fieldset, putting the individual hooks in an unordered list, and using CSS to format it into two columns.
2. Put this into a theme function so that I'm both a) not chucking hard-coded HTML into a form and b) allowing other people to format that however they see fit.