swift234

actually, just remove the "simple user defined datatypes" stuff.  The pattern matching
description subsumes most of it.  It was amusing that I thought (back in the day) as
structs as a special case of unions, but this isn't pertinent any more.

Rename the expressions.rst file.  It does have some useful stuff, but it should be merged
into other docs at some point.


Swift SVN r7359