choosing between various parser generators

[bstarynk]

the commit 166794d is supporting both ANTLR4 and GNU bison parser generators, with some buggy REPL (read-eval-print-loop) hand written parser ...

It is hoped that other contributors would decide which parser generator to use in RefPerSys.

The intent is that that parser generator will eventually be given as input (in 2023) some RefPerSys generated code, and will produce parsing code from some objects of the RefPerSys persistent store (in persistore/)