Crates which re-export types from other crates should also re-export the entire crate

[jsgf]

For example, quickcheck has:

extern crate rand;

pub use rand::Rng;

This has the problem that all users of quickcheck need to depend on the same version of rand as quickcheck if they want to use the rest of rand's API. If quickcheck had:

pub extern crate rand;

pub use rand::Rng;

then users can use quickcheck::rand to get access to the full rand API to interact with quickcheck, while not being constrained about what version of rand they want for their own purposes.

[jsgf]

https://users.rust-lang.org/t/rfc-api-guideline-re-export-a-whole-crate-if-exporting-any/17820

[WiSaGaN]

This issue has more discussion going on currently.

[KodrAus]

I'll close this one in favour of #176 to try keep discussion focused.