Support for -XPatternSynonyms

src/Haddock/Backends/LaTeX.hs

src/Haddock/Backends/Xhtml.hs

src/Haddock/Backends/Xhtml/Decl.hs

src/Haddock/Backends/Xhtml/Names.hs

src/Haddock/Convert.hs

src/Haddock/GhcUtils.hs

src/Haddock/Interface/Create.hs

src/Haddock/Interface/Rename.hs