rustc claims no_std is stable since 1.0.0

[nagisa]

src/lib.rs:11:12: 11:18 warning: this feature has been stable since 1.0.0. Attribute no longer needed, #[warn(stable_features)] on by default 
src/lib.rs:11 #![feature(no_std)]
                         ^~~~~~

but no_std was stabilised much later.

[nagisa]

This is an easy bug, involving an update of the version number in this list. Updating versions for other features is a bonus.