[Haskell] Idioms and Proposals

I've added a few Haskell idioms and proposals (well, ideas for changes) to the wiki: http://haskell.org/haskellwiki/Category:Idioms http://haskell.org/haskellwiki/Category:Proposals I particularly wanted to include "perennial" ideas that often seem to get discovered independently (for instance, type arithmetic). Of the proposals, I think only MonadPlus reform might be worth moving to the Haskell Prime process. Please add, improve, etc.