Docbook to latex conversion of the spec by Max Horn.

Docbook to latex conversion of the spec by Max Horn.

We now build the specification document from latex source instead of the
older docbook method since may developers have had trouble getting the
docbook tools to work. It's also faster.

For now, the built documentation is still kept in svn and rebuilt only
if --enable-docs is passed to configure. We may relax this to rebuilding
only if the tools are available once we're more confident it will work
with common TeX installations.

svn path=/trunk/vorbis/; revision=15748