Rm'd buildable files. New Makefile, palette-all

I removed the buildable file colorbrewer.tex. I additionally removed
palette-art.tex as I prefer to use a tex file that shows all the color
swatches so that I can browse for what I want to use. This occurs in a
new tex file called palette-all.tex.

I've added a Makefile to manage the building of colorbrewer.tex and
palette-all.pdf.