support chromepath, chromeopts, firefoxpath, and firefoxpref

[klrmn]

parser.add_option('--chromepath',
                 action='store',
                 dest='chrome_path',
                 metavar='path',
                 help='path to the google chrome driver executable.')
 parser.add_option('--firefoxpath',
                 action='store',
                 dest='firefox_path',
                 metavar='path',
                 help='path to the target firefox binary.')
 parser.add_option('--firefoxpref',
                 action='store',
                 dest='firefox_preferences',
                 metavar='str',
                 help='json string of firefox preferences to set (webdriver).')
 parser.add_option('--chromeopts',
                 action='store',
                 dest='chrome_options',
                 metavar='str',
                 help='json string of google chrome options to set (webdriver).')