generic ReadFile method

[corinwagen]

Right now if you want to write a script that reads in a variety of file types (e.g. Gaussian, Orca, etc), you have to do so in a loop:

mol = None
if filename.endswith(".inp"):
    mol = cctk.OrcaFile.read_file(filename).get_molecule()
elif filename.endswith(".gjf"):
    mol = cctk.GaussianFile.read_file(filename).get_molecule()
elif condition
    ...

It might be nice to write a function which simply takes in a file, tries all the methods (semi-intelligently), and then returns an object. Maybe you could choose between a method which always returns a File object and a method which always returns a Molecule object, reusing the same internals.