Refactor Haddock options
This patch renames the DOC_OPTIONS pragma to OPTIONS_HADDOCK. It also adds "-- # ..."-style Haddock option pragmas, for compatibility with code that use them. Another change is that both of these two pragmas behave like OPTIONS_GHC, i.e. they are only allowed at the top of the module, they are ignored everywhere else and they are stored in the dynflags. There is no longer any Haddock options in HsSyn. Please merge this to the 6.8.2 branch when 6.8.1 is out, if appropriate.