Syntax: Rewrite macro_rules

macro_rules failed in a lot of cases, this reworks it to fully support:
- Complete matcher syntax.
- Better bracket balancing support.
- Add `lifetime` designator (1.28).
- More resilient to odd syntax within the transcriber.  The content doesn't have
  to be Rust syntax, so it can sometimes get confused. Add a few escapes so it
  at least doesn't barf.
- At-most-once kleene operator (2018).

Author: ehuss