Add interpreting event parser proc to pegs module. (#8075)

* Added simple interpreting event parser to pegs module.
* Has side-effects problem.
* Macro solution works.
* First flat callback test works.
* Fixed namespace pollution.
* Added handler for pkChar.
* Replaced event parser test.
* Started extensive docs.
* 'callback' to 'handler' renaming part 1.
* Renaming 'callback' to 'handler' part2, completed comments.
* Fixed exported API pollution.
* Added more event handler hooks, fixed comments.
* Changed event parser addition entry.
* Fixed variable names and comments.
* Enhanced comment.
* Leave handlers are not called for an unsuccessful match.
* The three varieties of back-reference matches are processed in separate
of-clauses now.
* Improved hygiene and (almost) eliminated exports.
* Trying to fix CI test breakage by eliminating export.
* Trying to fix CI test breakage by eliminating exports.
* Re-activated leave handler code execution for unsuccessful matches.
* Eliminated the last export statement (with a funny smelling hack).
* Make sure leave handler code is executed for all unsuccessful matcher
cases.
* Replaced local unicode.`==` with export.

changelog.md

@@ -107,6 +107,7 @@
 - ``parseOct`` and ``parseBin`` in parseutils now also support the ``maxLen`` argument similar to ``parseHexInt``.
 - Added the proc ``flush`` for memory mapped files.
 - Added the ``MemMapFileStream``.
+- Added a simple interpreting event parser template ``eventParser`` to the ``pegs`` module.
 - Added ``macros.copyLineInfo`` to copy lineInfo from other node.
 - Added ``system.ashr`` an arithmetic right shift for integers.