PGF library: expose only PGF and PGF.Internal instead of all modules

PGF exports the public, stable API.
PGF.Internal exports additional things needed in the GF compiler & shell,
including the nonstardard version of Data.Binary.

src/compiler/GF/Grammar/Binary.hs

@@ -13,7 +13,7 @@ import Prelude hiding (catch)
 import Control.Exception(catch,ErrorCall(..),throwIO)
 
 --import Data.Char
-import Data.Binary
+import PGF.Internal(Binary(..),Word8,putWord8,getWord8,encodeFile,decodeFile)
 --import Control.Monad
 import qualified Data.Map as Map
 import qualified Data.ByteString.Char8 as BS
@@ -24,7 +24,7 @@ import GF.Infra.Option
 import GF.Grammar.Grammar
 
 import PGF() -- Binary instances
-import PGF.Data(Literal(..))
+import PGF.Internal(Literal(..))
 
 -- Please change this every time when the GFO format is changed
 gfoVersion = "GF03"

src/compiler/GF/Grammar/Grammar.hs

@@ -66,7 +66,7 @@ import GF.Infra.Option ---
 
 import GF.Data.Operations
 
-import PGF.Data (FId, FunId, SeqId, LIndex, Sequence, BindType(..))
+import PGF.Internal (FId, FunId, SeqId, LIndex, Sequence, BindType(..))
 
 --import Data.List
 import Data.Array.IArray

src/compiler/GF/Grammar/Printer.hs

@@ -29,8 +29,7 @@ import GF.Infra.Option
 import GF.Grammar.Values
 import GF.Grammar.Grammar
 
-import PGF.Data (ppMeta, ppLit)
-import PGF.Printer (ppFId, ppFunId, ppSeqId, ppSeq)
+import PGF.Internal (ppMeta, ppLit, ppFId, ppFunId, ppSeqId, ppSeq)
 
 import Text.PrettyPrint
 import Data.Maybe (isNothing)