* added mechanism for allowing use of different grammar-compilers /
-engines
  * moved code specific for grammar-compilation from SemanticInterpreter
to env/grammar/*
  * added several grammar-generators for grammar-compilers, including
the existing JS/CC-generator (moved the specific code from
GrammarConverter to the generator):
    available generators: JS/CC (default), Jison, PEG.js
  * added config property "grammarCompiler" for setting a specific
grammar-compiler (DEFAULT: "jscc"; see
SemanticInterpreter.setGrammarEngine() for possible values)