+ add very tests for output of very basic successful parse, in order to be able to catch things going wrong when common stuff is factored out
  (tests should be made much more flexible or removed entirely once refactoring is done)
* factor out overridden &publish_method_cache into InterceptedGrammarHOW
* factor out method &summary into InterceptedGrammarHOW (was a sub in Tracer...); it's now expecting both, the match object and the amount of indent
* factor out method &onRegexEnter into InterceptedGrammarHOW - unfortunately I can't seem to simply override it and use callsame in Debugger...?