Move tufte-latex material into main repo

Maintaining the tufte-latex repo as a subtree seems excessive and
unnecessary; we can just drop in the new files as we need them.
Move shared-repository material to this repo

I've move the shared preamble and bibtex database to this repository; while
the projects are under initial development it will be easiest to just
keep them separate.
Move copyright holders into separate AUTHORS.tex file

Obviously not important right now, since I'm the only copyright holder,
but this may be useful later and there's no reason to put it off.
Generate document date automatically

This commit removes the document date and version number from the repo
and generates it on-the-fly from the git repo as necessary.