Syntax definitions

SuperBASIC syntax is defined using a non-rigorous 'meta language' type notation.
Four type of constructions are used:
  |   |             select one of
  [   ]             enclosed item(s) are optional
  {   }             enclosed items are repeated (formal definition) or comment
  ..                range

e.g.   | A | B |    A or B
       [ A ]        A is optional
       { A }        A can be repeated
       A .. Z       A, B, C etc.
       {this is a comment}
