Add warnings flag

[aidanharris]

This commit adds a warnings flag

It can be combined with -q / --quiet to display warnings. The intent is to provide a silent option that still surfaces warning and error messages so that they are visible in logs.

I'm not entirely sure if this is the best approach or if there's already an existing way to accomplish this but with this I can run gallery-dl -q -w and I get silent output but still see warnings. Essentially, I want an option that's in-between -q and -v, -v is too noisy. I only want to see warning messages and error messages.

[mikf]

This is fine I think, but the help text should be a bit more specific - maybe "Print only warnings and errors" - and the option should be moved in-between -q and -v since it is, as you say, an option that's in-between -q and -v,

if there's already an existing way to accomplish this

There is, but having a shortcut cmdline option, especially if it's this simple, would be nice.