use parser combinators to parse the shell commands. simplified CommandLine type

GF.cabal

@@ -37,6 +37,7 @@ library
     PGF.Parsing.FCFG.Active
     PGF.Parsing.FCFG.Incremental
     PGF.Parsing.FCFG
+    PGF.ExprSyntax
     PGF.Raw.Parse
     PGF.Raw.Print
     PGF.Raw.Convert
@@ -79,9 +80,6 @@ executable gf3
     GF.Source.PrintGF
     GF.JavaScript.AbsJS
     GF.JavaScript.PrintJS
-    GF.Command.LexGFShell
-    GF.Command.AbsGFShell
-    GF.Command.PrintGFShell
     GF.Infra.CompactPrint
     GF.Text.UTF8
     GF.Data.MultiMap
@@ -91,8 +89,6 @@ executable gf3
     GF.Infra.PrintClass
     GF.Compile.GenerateFCFG
     GF.Data.ErrM
-    GF.Command.ParGFShell
-    GF.Command.PPrTree
     GF.Source.ParGF
     GF.Data.Operations
     GF.Infra.Ident
@@ -104,6 +100,9 @@ executable gf3
     GF.Infra.UseIO
     GF.Command.Commands
     GF.Command.Interpreter
+    GF.Command.Abstract
+    GF.Command.Parse
+    GF.Command.Importing
     GF.Infra.Modules
     GF.Grammar.Grammar
     GF.Source.GrammarToSource
@@ -139,7 +138,6 @@ executable gf3
     GF.Source.SourceToGrammar
     GF.Compile.GetGrammar
     GF.Compile
-    GF.Command.Importing
     GF.System.Readline
     PGF
     PGF.CId