Added binary numeral grammars.

examples/numerals/BinaryDigits.gf

@@ -0,0 +1,11 @@
+concrete BinaryDigits of Binary = {
+
+flags startcat=Bin ;
+
+lincat Bin = { s : Str } ;
+
+lin End = { s = "" } ;
+lin Zero b = { s = "0" ++ b.s } ;
+lin One b = { s = "1" ++ b.s } ;
+
+}