Move shared rule pointer factories into individual rule files

todo.md

@@ -0,0 +1,36 @@
+TODO
+====
+
+# complete the list of rule types
+
+- add repeat rules
+- parse regex rules into trees of choices, sequences, repeats
+
+# generate lexers for sets of terminal rules (can be mix of throwaway and meaningful)
+
+Introduce ParseTable type which contains a vector of ParseStates. A ParseState contains a
+TransitionMap of ParseActions. For a lexer, a ParseAction can be one of:
+    - Accept(symbol)
+    - Advance(state index)
+
+Then generate a C function for a ParseTable
+
+# generate parsers from sets of non-termina rules
+
+For a Parser, the ParseActions can be any of:
+    - Accept(symbol)
+    - Shift(symbol)
+    - Reduce(symbol, number of child symbols)
+    
+# normalize grammars
+
+- add concept of throwaway-terminals (tokens that won't appear in constructed AST)
+- classify rules as non-terminals or terminals
+- extract strings and regexes from non-terminal rules into their own throwaway-terminals,
+    in order to separate lexing from parsing
+
+After this, a grammar will have these fields:
+- non-terminal rules
+- terminal rules
+- throwaway terminal rules
+