Rename --disallow-untyped-defs to --disallow-any=unannotated

[ilinum]

Previously, we were talking about naming this flag was --disallow-any=untyped. However, I think it's not clear without knowing the old name of the flag (--disallow-untyped-defs).

Naming suggestions are very welcome!

[JelleZijlstra]

Honestly I prefer the old name; I find it much easier to understand what it does, because I don't have to think about the fact that unannotated defs implicitly use Any.

[gvanrossum]

I'm with Jelle. I know Stas wants to use the new flag style. Let's have the old and the new name together for a while -- personally I expect that we haven't come up with the best API for these checks.

[ilinum]

I definitely see your point: --disallow-untyped-defs is more understandable than --disallow-any=unannotated

However, the idea behind --disallow-any option is to have one way to control all Anys in your code and we should have some way of disallowing untyped defs with the new flag.

That being said, I'm okay with the idea of having both of them co-exist.

[gvanrossum]

OK, please do that.

[ilinum]

@ddfisher this PR is ready for review.

[ddfisher]

LGTM!

The flag aliasing is unfortunate, but I think it's the right thing for now.