Introduce type RawIdent; only 9 imports of Data.ByteString.Char8 remain

The fact that identifiers are represented as ByteStrings is now an internal
implentation detail in module GF.Infra.Ident. Conversion between ByteString
and identifiers is only needed in the lexer and the Binary instances.

src/compiler/GF/Grammar/Binary.hs

@@ -34,7 +34,7 @@ instance Binary Ident where
   get    = do bs <- get
               if bs == BS.pack "_"
                 then return identW
-                else return (identC bs)
+                else return (identC (rawIdentC bs))
 
 instance Binary SourceGrammar where
   put = put . modules
@@ -289,6 +289,9 @@ instance Binary Label where
              1 -> fmap LVar   get
              _ -> decodingError
 
+instance Binary RawIdent where
+  put = put . rawId2bs
+  get = fmap rawIdentC get
 
 putGFOVersion = mapM_ (putWord8 . fromIntegral . ord) gfoVersion
 getGFOVersion = replicateM (length gfoVersion) (fmap (chr . fromIntegral) getWord8)