based on the old PR by @dragostis: pest-parser#277

Changes that were made:
- debugger core context was refactored and extracted to a lib (so that
it could be used in other frontends, e.g. editor plugins)
- CLI was extended using rustyline helpers to provide file completions,
history etc.
- applied suggestions from @hansihe from the old PR
(pest-parser#277 (comment)):
1. added `ba` (add breakpoints at all rules) which is useful
for stepping through the entire grammar, plus breakpoint deletions
and loading input directly from readline;
2. added command line arguments.
- changed the listener function to return a boolean, so that
the debugger can signal back to a parsing thread to finish
before reaching its input's EOF.

Co-authored-by: Dragoș Tiselice <dragostiselice@gmail.com>