Modify pageNumberLookup.rb script to (a) link C language references to (#65)

opencl-2.0-openclc.pdf, which in turn links to the current asciidoctor
OpenCL C 2.0 PDF and (b) not rewrite the link to land on specific page
numbers, some of which were out of date.

Regenerate HTML pages accordingly.

Note that the '#namedest=<entry point name>' xrefs are still present in
the PDF hyperlinks, since they're not rewritten - but they do nothing,
since the PDFs / PDF readers don't support the namedest syntax.

Fixes https://github.com/KhronosGroup/OpenCL-Docs/issues/87 .