A couple of tidy-up patches. Add some comments/haddock and rename
type-variables for legibility.
2 patches for repository http://darcs.net:
Tue Feb 21 02:24:39 GMT 2012 Owen Stephens <darcs@owenstephens.co.uk>
* Add comments/haddock to Patch/Set.hs
Tue Feb 21 02:27:35 GMT 2012 Owen Stephens <darcs@owenstephens.co.uk>
* Clean up type-variables in signatures of Patch/Set.hs