pytraj.txt: pytraj license (GPL v3)

But if you would like to reuse code snippets and pieces independent of cpptraj, I am (Hai) happy to license them (pieces of codes) under 
BSD-2 Clause or whatever you like. Just buzz us.

externals: licenses for external libs we used
    + six.txt: six.py (BSD)
    + magic.txt: magic package (MIT)
    + pandas.txt: pandas package ("new" BSD)
    + dask.txt: dask package (new BSD): used in ../pytraj/datasets/DataSet_1D.pyx
    + toolz.txt: toolz package (BSD): copy/adapt several functions
    + mdtraj.txt: BSD-2 for adapting setup process.
