Tweaks to help resolve ambiguity / infinite recursion.
Tweaks to help resolve ambiguity / infinite recursion.

* Avoid having empty lists of expressions ever be valid. As a consequence...

* Add an explicit `emptyListlet` rule.

* Add an explicit no-arg variant to the `call` rule. This makes
  `blort()` be the form of a no-arg call, rather than trying to get
  cheeky with Lisp-like parenthesization, the latter which seemed to
  be causing too much trouble.

* Also, did a minor rearrangement of the rules for clarity.

danfuzz/samizdat,danfuzz/samizdat,danfuzz/samizdat,danfuzz/samizdat