Merge branch 'experimental'

I'm not entirely happy with the new paragraph heuristics, but I've been
using them for a while and have grown used to them and have grown to
rely on the behavior.  Since there probably aren't all that many other
people who use uemacs, let's just merge that behavior and see if anybody
else even notices.

The "NBSP to SP on keyboard input" is similarly convenient to me, and
might be offensive to others.  Let's see.

* experimental:
  Turn NBSP into regular SP on input
  Try updated rule for "is new paragraph"
  Make some minor code legibility changes