Makefile updates

I made a few updates to the Makefile so that it operates more correctly. For one, it was broken if you just tried to run 'make', as the default target was the $(DVI) target, which didn't know how to build the whole document correctly (with bibtex references and everything).

So, I rewrote the dependencies as best as I good.

Further improvements could be made by switching to the pdflatex processor (required if, for instance, you're including any PDFs as figures -- I personally use this for including .dot graphs rendered with graphviz) instead of just latex. But I left things as-is to remain "simple."

Cheers.