Goals:

• Deprecate --best-stream-default and replace it with --default-stream <stream>.
• Add --stream-url option to print the URL used by --player-passthrough.
• Add plugin specific config, e.g. ~/.config/livestreamer/config.twitch would be applied on top on the regular config when accessing Twitch URLs.
• Add structure validation to the plugin API.
• Add some sugar methods to the API: livestreamer.streams(url), session.streams(url) and plugin.streams().
• Moderinze/refactor old plugins to newer standards and APIs.