Language idea: Consider removing the mandatory mod directive

[alexrp]

Is there actually a good reason to have this in the language? Module lookup is probably not going to need it at all. Right now, the only function it serves is being able to attach certain well-known attributes to it. Perhaps we could find a different way to do that.

[alexrp]

mod {
    pub fn add(x, y) {
        x + y;
    }
}

Approved for 1.0.