pngtex-simplification

  - CLEANUP: using tempfile.mkdtemp() to make temporary directory
  - CLEANUP: combining the docclass/begindoc/enddoc to a single file template.tex
  - BUGFIX: adding the missing math mode for the formula
  - CLEANUP: using the cwd-parameter to call() rather than setting state with chdir()
  - FEATURE REMOVAL: removed the "packages"/"source" dir for latex --- simplifies things slightly; if it was/is actually used, then remoning it would be a problem...