Allow for customized primary in ExpressionParser

[jdrem]

Some languages may have rules like:

expression : logicalExpression (logicalOp logicalExpression)?

logicalExpression : relation (relationalOp relation)?

relation : term (addOp term)?

term : factor (multOp factor)?

factor : (unaryOp) primary

primary : instantiation | variable | functionCall | literal     

instantiation : NEW ( namespaceIdentifier '.')? className 
     '(' (expression ( ',' expression ))? ')'
                                                      
functionCall :  identifier '(' (expression ( ',' expression))? ')'

How would you handle the instantaion or function call? We'd need to add customization so
these can be lexed/parsed as a primary element of the expression.