[antlr-interest] ENHANCEMENT: Add invoke(...) method(s) on parser

[Austin Hastings]

While it's possible to do "different" things with the generated parsers, 
especially tree parsers, there aren't *that* many different things 
possible. I'd like to suggest generating an "invoke()" method that calls 
the top-level production.

There might be several signatures - invoke on File, on String, on 
Stream, but the basic paradigm of

CharStream input = ANTLRxyzStream(whatever);
CommonTokenStream tokens = new CommonTokenStream(new 
$grammarName$Lexer(input));
$grammarName$Parser parser = new $grammarName$Parser(tokens);
$methodName$_result result = parser.$methodName$();

is too much of a gimme not to be autogenerated. Of course, there's a 
potential option or antlr grammar change there, to indicate the "main" 
target. If not, then the first one in the file seems obvious.

=Austin