jao's string foo

Ok... all merged up.  Great work.  Thanks especially for the doc
updates, simplifications to various code, invariant strengthening,
test suite updates, and overall evident attention to detail in what is
some pretty twisted code.   I do need to overhaul rx at some point to
catch up to Unicode foo.

I had been thinking it might be necessary to, in the short term, just
support iso8859-1 strings in Pika but, no, we're well within shooting
range of a full Unicode string type.

Next stage plans coming up soon.

Thanks,
-t