update licenses

Accept Ioannis Filippidis's advice.
change the licenses.
add working enviroment
Merge branch 'master' of https://github.com/valbendan/pycflow2dot
line numbers, argparse, latex hyperref linking

functions defined in file have their line numbers included in the nodes
argparse now used
half-way through hyperref linking between calls and defs for
multi-page pdf output for multiple src files, using LaTeX
updated readme
added GPL license text