It now takes a context pointer (opaque data) that holds the buffers it
uses for the temporary strings. If the context pointer is null, a static
context is used (making those uses of va NOT thread-safe). Most calls to
va use the static context, but all such calls have been formatted
consistently so they are easy to find when it comes time to do a full
audit.
I had messed up my index array creation, but once that was fixed the
textures worked well other than a lot of pixels are shades of grey due
to being in the top or bottom color map range.
