- rename `in_rules_failure_analysis_mode` to `__in_rules_failure_analysis_mode__` to signal that this 'option' is purely INTERNAL USE ONLY.
- rename `in_rules_failure_analysis_mode` to `__in_rules_failure_analysis_mode__` to signal that this 'option' is purely INTERNAL USE ONLY.

- preliminary work done, copied from a performance tuned lexer instance, to start lexer optimizations like the ones done in jison itself, where unused code is removed from the parser (here: *lexer*) run-time kernel in order to speed things up at parse/lex run-time. The current code works as before: all tests pass.

GerHobbelt/jison-lex,GerHobbelt/jison-lex