bring down below 102 lines
Change the semantics for _!_ variables when they are under ellipses

In particular, make the semantics less insane. There is now a
much simpler description of how these two interact (see docs)

Altho this is a backwards incompatible change, it seems relatively
unlikely to affect anyone negatively and it makes the R6RS semantics
better and makes it possible to think about enumerating expressions
from that grammar