Add option to ignore config files

[jaimeMF]

That way if you have set in your config files to use title or other option in the output files, and you specify an output template on the command line, the template is used and you don't get the error: using output template conflicts with using title, video ID or auto number.

[phihag]

While I like the option, we should just fix the bug you mention.

[jaimeMF]

I don't think it's a bug, what option would you give more importance: the template or the other options?

[phihag]

The latter one, whichever that is. So we should go ahead and for each list of arguments parse -t, --id, -o and friends, and override the previous configuration.

[jaimeMF]

Does optparse give the order of the options?

[phihag]

Sorry, that wasn't well-expressed. I mean that options in the user configuration file override options in the system config file, and option in on the command-line override options in the configuration file (within reason). The parsing process should go like

default_settings = {'template': '%(id)s.%(ext)s'}
settings = default_settings.copy()
args = readArgs('/etc/youtube-dl.conf')
settings.update(parseArgs(args, errmsg='invalid system configuration'))
args = readArgs('~/.config/youtube-dl.conf')
settings.update(parseArgs(args, errmsg='invalid user configuration'))
settings.update(parseArgs(sys.argv))

[jaimeMF]

That makes sense, but would it still complain when both template and other option is given on the command line, or would it choose one of them?

[phihag]

It would still complain, unless we change that behavior too. I see little reason of why we would that though.

Documented these issues in #632 and #633.