[Haskell] Idioms and Proposals

[Ashley Yakeley]

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.