Remove completed todo items

todo.md

@@ -4,11 +4,8 @@ TODO
 ### Handling ambiguity (GLR)
 * Add a simple way to specify syntactic ambiguity resolutions in the Grammar (e.g. 'prefer declarations to statements' in C), similar to bison's `dprec`
 construct.
-* Optimize the lexical DFA so that all compatible starting lex states are merged. Then, when the parse stack has multiple heads, check at runtime that each head's state corresponds to the same starting lex state.
 
 ### Runtime System
-* Don't automatically reparse on every edit; expose a separate function for
-  explicitly reparsing, so that multiple related edits can be made cheaply.
 * Refactoring: make separate symbol for unexpected characters than for interior error nodes.
 
 ### Testing / Quality
@@ -33,5 +30,3 @@ construct.
   - [ ] Parsing returns control to parent language
 * Indentation tokens
 
-### Performance
-* Optimize grammar compilation