Make empty argument lists optional

[jgrosso]

This might require having where bindings be wrapped in an extra set of parentheses, so as to avoid ambiguities between the optional argument list, required function body, and optional where-bindings. To fix this, we'll change (= foo args ...) to (= (foo args) ...) (which has the added benefit of matching how functions are defined in Common Lisp etc., and even – in a sense – Haskell!).