Use const generics in ArrayVec

[bluss]

Use const generics for ArrayVec and ArrayString - now it can support arbitrary capacity/backing array.

Syntax changes like this:

• old: ArrayVec<[T; CAP]>
• new: ArrayVec<T, CAP>
• old: ArrayString<[u8; CAP]>
• new: ArrayString<CAP>

The ArrayVec<T, const CAP: usize> for now always uses an usize for its length, and so uses more space than the old ArrayVec<[T; CAP]>.

Requires Rust 1.51 (March 2021)

In for example Vim one can use the following substitution to update syntax:

:%s/ArrayVec\(:\?:\?\)<\[\(.*\);\(.*\)\]>/ArrayVec\1<\2,\3>/g

Fixes #125
Closes #100

[bluss]

CI passes on beta and nightly - will pass fully when Rust 1.51 is released this week.

[WiSaGaN]

The ArrayVec<T, const CAP: usize> for now always uses an usize for its length, and so uses more space than the old ArrayVec<[T; CAP]>.

I am wondering if rust-lang/rust#76560 can help with the size regression introduced here in future version of ArrayVec?

[bluss]

Later PR updated the length to always be u32 (for a smaller size). I can't answer your question, maybe you know? 🙂

[WiSaGaN]

It seems so to me, but I am not terribly familiar with Rust constant generics. Will try push a pull request when it is stable!