perlapi: Include general information

Unlike other pod handling routines, autodoc requires the line following
an =head1 to be non-empty for its text to be included in the paragraph
started by the heading.  If you fail to do this, silently the text will
be omitted from perlapi.  I went through the source code, and where it
was apparent that the text was supposed to be in perlapi, deleted the
empty line so it would be, with some revisions to make more sense.

I added =cuts where I thought it best for the text to not be included.
perlapi: Refactor placements, headings of some functions

It is not very user friendly to list functions as
"Functions found in file FOO".  Better is to group them by purpose, as
many were already.  I went through and placed the ones that weren't
already so grouped into groups.  Patches welcome if you have a better
classification.

I changed the headings of some so that the important disctinction was
the first word so that they are placed in the file more appropriately.

And a couple of ones that I had created myself, I came up with a name
that I think is better than the original
perlapi: Place in dictionary sort order

Underscores or their lack can confuse people in finding sorted items.