Parse and check the command line arguments.

def main(argv=sys.argv):
    # type: (List[str]) -> int
    """Parse and check the command line arguments."""
    parser = optparse.OptionParser(
        usage="""\
usage: %prog [options] -o <output_path> <module_path> [exclude_pattern, ...]

Look recursively in <module_path> for Python modules and packages and create
one reST file with automodule directives per package in the <output_path>.

The <exclude_pattern>s can be file and/or directory patterns that will be
excluded from generation.

Note: By default this script will not overwrite already created files.""")

    parser.add_option('-o', '--output-dir', action='store', dest='destdir',
                      help='Directory to place all output', default='api')
    parser.add_option('-s', '--source-dir', action='store', dest='srcdir',
                      help='Documentation source directory', default=BASEDIR)
    parser.add_option('-n', '--docname', action='store', dest='docname',
                      help='Index document name', default='api')
    parser.add_option('-l', '--follow-links', action='store_true',
                      dest='followlinks', default=False,
                      help='Follow symbolic links. Powerful when combined '
                      'with collective.recipe.omelette.')
    parser.add_option('-P', '--private', action='store_true',
                      dest='includeprivate',
                      help='Include "_private" modules')
    parser.add_option('--implicit-namespaces', action='store_true',
                      dest='implicit_namespaces',
                      help='Interpret module paths according to PEP-0420 '
                           'implicit namespaces specification')
    parser.add_option('--version', action='store_true', dest='show_version',
                      help='Show version information and exit')
    parser.add_option('--clean', action='store_true', dest='cleanup',
                      help='Clean up generated files and exit')
    group = parser.add_option_group('Extension options')
    for ext in EXTENSIONS:
        group.add_option('--ext-' + ext, action='store_true',
                         dest='ext_' + ext, default=False,
                         help='enable %s extension' % ext)

    (opts, args) = parser.parse_args(argv[1:])

    # Make this more explicitly the current directory.
    if not opts.srcdir:
        opts.srcdir = '.'

    if opts.show_version:
        print('Sphinx (sphinx-apidoc) %s' % __display_version__)
        return 0

    if opts.cleanup:
        print("Removing generated API docs from '{}'...".format(opts.srcdir))
        return cleanup_api_docs(opts)

    if not args:
        parser.error('A package path is required.')

    opts.rootpath, opts.excludes = args[0], args[1:]
    return generate_api_docs(opts)