Work in progress on translating linearization functions to Haskell

The translation is currently good enough to translate all concrete syntaxes
of the Foods and Letter grammars, and some concrete syntaxes of the Phrasebook
grammar (e.g. PhrasebookEng & PhrasebookSpa works, but there are problems with
e.g. PhrasebookSwe and PhrasebookChi)

This functionality is enabled by running

	gf -make -output-format=haskell -haskell=concrete ...

TODO:
	- variants
	- pre { ... }
	- eta expansion of linearization functions
	- record subtyping can still cause type errors in the Haskell code
	  in some cases
	- reduce code large tables

gf.cabal

@@ -175,6 +175,7 @@ Library
     GF.Compile.Multi
     GF.Compile.Optimize
     GF.Compile.PGFtoHaskell
+    GF.Compile.ConcreteToHaskell
     GF.Compile.PGFtoJS
     GF.Compile.PGFtoLProlog
     GF.Compile.PGFtoProlog