Local parsers

There are many scenarios we want to support where we need to update the parsing table while we are parsing.
Examples:
1- def + notation macro that allows us to define functions and notation simultaneously.

def (_++_) {a} : List a -> List a -> List a
| [], bs => bs
| a::as, bs => a :: (as ++ bs)

2- Recursive macros. The following macro definition works as expected

syntax "repeat " tactic : tactic

macro_rules
| `(repeat $tac) => `(tactic| ($tac; repeat $tac) <|> skip)

but, the following one does not

macro "repeat " x:tactic : tactic => `(($x; repeat $x) <|> skip)

The problem is that the syntax repeat x does not exist yet when we are parsing `(($x; repeat $x) <|> skip)

No files or tests are named. Start by locating the parser and macro-expansion entry points that maintain the parsing table, then use the two examples to determine how local updates and recursive macros should behave. Done means both examples parse and expand as described, with regression coverage.