Minor updates to tex source and gitignore
Now using latexmk; pt-BR punctuation is working

I switched pdflatex for latexmk in the Makefile in order to use the `-c`
flag, which deletes the extra files generated during compilation. Neat.

Also, after changing the packages `babel` and `inputenc` to use,
respectively, `portuguese` and `utf8`, using LaTeX punctuation escapes
is unnecessary. This means editing this file will become much more
pleasurable from now on (or so I hope).