More work on the canonica_gf export

+ Abstract syntax now is converted directly from the Grammar and not via PGF,
  so you can use `gf -batch -no-pmcfg -f canonical_gf ...`, to export to
  canonical_gf while skipping PMCFG and PGF file generation completely.
+ Flags that are normally copied to PGF files are now included in the
  caninical_gf output as well (in particular the startcat flag).

gf.cabal

@@ -186,7 +186,7 @@ Library
     GF.Compile.Multi
     GF.Compile.Optimize
     GF.Compile.PGFtoHaskell
-    GF.Compile.PGFtoAbstract
+--  GF.Compile.PGFtoAbstract
     GF.Compile.PGFtoJava
     GF.Haskell
     GF.Compile.ConcreteToHaskell