Proposed change to macro parameter syntax

[popematt]

Proposed change:

• Parameter types are no longer grouped in a s-expression (e.g.: (foo int))—the type is annotated on the parameter name (e.g. int::foo)
• A grouped parameter is indicated by putting [] around the variable name (e.g. [foo]). When the variable has a type annotation, the type annotation stays with the variable name (e.g. [int::foo]).

@toddjonker's response from #287

Removing the S-expression from parameter type declarations eliminates a critical extension point. As an annotation, there's no good way to do anything but a type-name.

[popematt]

@toddjonker What sort of parameter modifiers do you anticipate having aside from a type name, grouped-ness, and cardinality?