perlapi: Refactor placements, headings of some functions

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