Handle shebang (#!) lines

[corranwebster]

Code with an executable escape at the start does not validate correctly. Eg.

#! /usr/bin/env python

# (C) Copyright 2005-2020 Enthought, Inc., Austin, TX
# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in LICENSE.txt and may be redistributed only under
# the conditions described in the aforementioned license. The license
# is also available online at http://www.enthought.com/licenses/BSD.txt
#
# Thanks for using Enthought open source!

gives an error H103 Wrong copyright header found.

This occurs mainly in example and demo files which are intended to be run stand-alone (although, as an aside, many of these don't have the execute flag set as would be needed to make the shebang work).

For reference, although the shebang is a Unix convention, Python provides support for the most common patterns on Windows. See https://docs.python.org/3/using/windows.html#shebang-lines

It may be sufficient to optionally allow #! /usr/bin/env python #! /usr/bin/env python3 to precede the copyright header, as all other shebang lines are almost certainly not what we would want for demos.