`aes-ctr` has been merged into the `aes` crate

Please use the `aes` crate going forward. The new repository location is at:

<https://github.com/RustCrypto/block-ciphers/tree/master/aes>

The `aes` crate now has an optional `ctr` feature which autodetects SIMD
features on `i686`/`x86-64` targets and uses them if available, or otherwise
falls back to the implementation in the `ctr` crate.

If you would prefer not to have this autodetection performed, use the `aes`
crate directly with the `ctr` crate.