[initiate] is called from [reduce] which can be called from [error_reduce],
so [env.token] CAN be [error_token].

Surprisingly, this SPEEDS things up. Now, table / code = 2.0.

Changed & to && in tarjan.ml.

The power of magic!

that it does not write [env.current]. This was easy, as the write
to [env.current] was in fact unobservable and could be replaced
with a write to a local reference [current]. At the same time,
changed the local recursive function [pop] to a loop, for greater
readability.

Added a few new test inputs.

Added trustme.sh to re-generate the reference outputs.

for updating [env.stack]. Instead, it returns the new stack.
This corresponds to Frédéric's "Isolate side-effects from table-backend generated code".

This is a copy of the calc demo, plus a script that runs the parser
in three different modes (code, table, reference interpreter) and
checks the results.

no longer uses [Error.signal].