Change ifs to whens when there's no else.

Also, fns that require default collector args are
now multiarity, so that calls don't have to know
about them.
Not= returns a boolean itself.
Cleanup map, reduce, and recursive fns.
Destructure args in a more obvious way.
Kill tuples-to-hash with fire.
Merge nested let statements.
Simplify map fn.
Whitespace.