Merge branch '0.9.4-changes'

Actually bump proptest-derive to 0.1.2.

Proptest version 0.9.3, proptest-derive 0.1.1.

Proptest version 0.9.3, proptest-derive 0.1.1.

Merge branch '0.9.2-changes'

Fix adding outdated note to old docs versions.

Merge branch '0.9.0-changes'

Version 0.8.7.

Version 0.8.6.

Fix more references to nonexistent nightly features.

A couple only make sense with `std` now apparently.