change BNF (but not implementation of BNF) for parsing, to handle layers, and also change minimum key in layer tree to be 1

fcore/parser/brace-dfa.sml

@@ -5,8 +5,13 @@ struct
   val final = 2
 
   fun makeStart i =
-    let val chr = Char.chr i
-    in if chr = #"{" orelse chr = #"}" then final else dead
+    let
+      val chr = Char.chr i
+    in
+      if chr = #"{" orelse chr = #"}" orelse chr = #"[" orelse chr = #"]" then
+        final
+      else
+        dead
     end
 
   val deadTable = SpaceDfa.deadTable