Heterogeneous AST node types

I just finished adding heterogeneous AST node types to the tree construction. I did not get a response on the mailing list about what people needed, so I build what I thought I would need. The mechanism is extremely simple. If you want a specific node type for a token type, simply switch on the token type inside the TreeAdapter. When you need to use a specific node type for the same token type depending on grammatical context, then ANTLR needs to let you specify that. Here's a simple example that illustrates how to set the node type for token references and string literals:

a : ID<Var> ID<Method> 'main'<Method> ;

This will also work with the rewrite operator. Any token or string literal on the right-hand side can specify the node type, including arguments if necessary:

// imaginary node
m : type ID '(' args ')' body -> ^(METHOD<MethodNode> type ID args body) ;

// real node
d : type ID ';' -> ^(DECL type ID<VarNode>) ;

Can use literals too:

a : 'int' -> 'int'<TypeNode> ;

Args just get passed to constructor:

b : ID -> ID<VarNode>[3,4] BLORT<IckNode>["hi"];

Can even do in loops:

g : ID+ -> ID<VarNode>+ ;

Cool, eh? This is all still in my dev branch. My intention is that this will be used in rewrites for tree grammars too, but not on left side of -> in tree grammars.

In terms of implementation, ID<Var> becomes new Var(ID) and ID<Var>[foo] becomes new Var(ID, foo) instead of the usual stream_ID.next() etc...