Conditionally include subscriber

[briankung]

Per my reddit comment:

I guess the only other thing is to be able to subscribe to console with an attribute or something. I wanted to conditionally include the subscriber (maybe in debug profile?) but ended up doing something like if cfg!(features = my-custom-feature) { console_subscriber::init(); }. Not ideal and my exact feature request might not be something you'd want for everyone, but something along those lines might be nice.

Thanks for a great crate!