pytao --help fails as no lattice/init file is specified

[ken-lauer]

A special case for the CLI entrypoint is --help, which should show the same information as tao --help.

With #93, we now require a lattice or init file in order to initialize a pytao.Tao object, just as tao itself would require.
Because of that, pytao --help fails:

$ pytao --help
pytao.tao_ctypes.util.TaoInitializationError: Tao will not be able to initialize with the following settings:

init='--help'

This should be special-cased in the CLI to print out the help text and exit.