Add a list of contributors to the user guide
Add a list of contributors to the user guide

Break out everyone thanked in the `Acknowledgements` chapter into a
separate contributor list and add everyone from `darcs show authors`.
We consider everyone who is thanked to be a contributor as a conservative
estimation :-)

I have added some more contributors that I know about, who were not in the
darcs history, but others may be missing. So please add anyone that you think 
is missing from the list.

ghcjs/haddock-internal,ghcjs/haddock-internal