Final review before 1.0

[Nugine]

The current APIs are nearly stable.

Remaining questions:

• [x] rlimit will not add cgroups API. cgroups-rs is recommanded now.
• [x] Is it ok to use u64 as the rlim type for all platforms? (Yes)
• [ ] The signature of rlimit::prlimit seems sightly strange. Is there a better way?
• [ ] setmaxstdio(u32::MAX) can lead to crash. Should it be a feature or a bug?

Related issues:

• [ ] https://github.com/rust-lang/libc/issues/2724