bugfix: -l and -t options were swapped

The -l and -t options to pydflatex would update each other's
state. This has been fixed.

Signed-off-by: Jeremy C. Andrus <jeremya@cs.columbia.edu>
support more complicated LaTeX options

For larger LaTeX projects, it is often advantageous to invoke
pdflatex using a more complicated command line. For instance,
the following commands can be built using options to a Makefile:

pdflatex \let\ifdraft\iftrue \let\ifextracompress\iftrue \input{proj.tex}

This patch allows pydflatex to accept additional pdflatex options
which replace the single tex file option. To allow pydflatex to parse
the output of the pdflatex build described above, you would use:

pydflatex [OPTIONS] proj.tex \let\ifdraft\iftrue \let\ifextracompress\iftrue \input{proj.tex}

Signed-off-by: Jeremy C. Andrus <jeremya@cs.columbia.edu>
add the ability to invoke bibtex instead of pdflatex

This is handy when pydflatex is used from Makefiles for larger projects.
There is currently no log parsing for BibTeX output, but the tool can
now be invoked using "pydflatex -b"

Signed-off-by: Jeremy C. Andrus <jeremya@cs.columbia.edu>