* `define-infix*` permits the declaration of greedy infix operators that receive all right hand side elements of the expression
* `:=` now also accepts non-infix expressions on the right hand side and auto-wraps them
* simplify recognizing infix expressions: a second expression value matching an infix symbol triggers infix parsing. Otherwise the list is not treated as an infix expression. This also allows us to define greedy infix operators.