new modules to make model .dat files for sncosmo

      * mk_sncosmo_model.py : convert contents of Whalen .tar.gz file into
         a single SED file that can be imported into sncosmo.
      * sncosmo_demo.py : demonstration of how to load a popIII model
        and make a light curve plot from it.
      * also added .gitignore and __init__.py