[aldonius]

I see it not so much as getting the compiler to ignore semver but rather giving it more granular information about the nature of the changes.

As I understand it:

- Anything which is breaking-changed in any way for 0.3.0 (e.g. in the article a type change from i32 to u32) is the exact same code in 0.2.1 as it was in 0.2.0.

- Anything which stays the same for 0.3.0 is re-exported in 0.2.1 (from 0.3.0). The code is replaced with a `pub use ...;`

- Anything which moves around in the submodule hierarchy (but is otherwise unchanged) in 0.3.0 is re-exported in 0.2.1, from where it used to be.

If crate Baz depends on something in Foo 0.2.x which changes in Foo 0.3.0, then when (if!) Baz updates to Foo 0.3.0 it will need to deal with that. But Baz can upgrade to Foo 0.2.1 without concern, and any types unchanged in Foo 0.3.0 will be interoperable.