Support twitch-cli env file

[hardliner66]

When using the official twitch-cli it will store it's token in ~/.twitch-cli/.twitch-cli.env. We should probably use that file if it exists, so you wont need to login twice.

[ModProg]

While should support that, what would be the best place to store our own token?

.config/twitchctl/config.smth

[hardliner66]

@ModProg we should probably also respect the XDG_CONFIG_HOME env var, if we want to do it properly.

[ModProg]

@ModProg we should probably also respect the XDG_CONFIG_HOME env var, if we want to do it properly.

Already happening, using https://docs.rs/dirs/3.0.2/dirs/