Previously, we attempted to completely separate the parse states
for item sets with non-terminal extras from the parse states
for other rules. But there was not a complete separation.
It actually isn't necessary to separate the parse states in this way.
The only special behavior for parse states with non-terminal extra rules
is what happens at the *end* of the rule: these parse states need to
perform an unconditional reduction.
Luckily, it's possible to distinguish these *non-terminal extra ending*
states from other states just based on their normal structure, with
no additional state.
* Structure `cli` crate as both a library and an executable, so that
benchmarks can import code from the crate.
* Import macros in the Rust 2018 style.
