cfg-vis

A macro to support #[cfg()] on visibility.

```rust use cfgvis::{cfgvis, cfgvisfields};

// default visibility is pub, while the target is linux, the visibility is pub(super).

[cfgvis(targetos = "linux", pub(super))]

pub fn foo() {}

[cfgvisfields]

pub struct Foo { #[cfgvis(test, pub)] pubintest: i32, #[cfgvis(test)] pub prvintest: i32, } ```