The addRules method may exceed the 64KB limit for bytecode. Generate
two methods instead: addRules1  and addRules2.

Tokens are allowed to be metavariables, but they do not need to
be wrapped in a MetaVariable node. Handle this case in the generated
buildMetaVar method.

We want to be able to import the Java grammar into the Earley Parser test
suite. In order to do that, we need to avoid references to external classes
in the parser spec.

The metavariable introduction was modelled as constraint problem to reduce
the number of metavariable productions as much as possible. This didn't work
well with lists and we introduced more GAP productions than neede. Since
the parser is faster now, we don't have to reduce the number of metavariable
productions.

Generate a method that builds the correct AST MetaVariable or Gap
based on the symbol in the concrete syntax tree.

Introduce the visit() function that is meant to transform a PEP
tree node to a JastAdd node.