`aes-soft` 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>

AES-NI is now autodetected at runtime on `i686`/`x86-64` platforms.
If AES-NI is not present, the `aes` crate will fallback to a constant-time
portable software implementation.

To force the use of a constant-time portable implementation on these platforms,
even if AES-NI is available, use the new `force-soft` feature of the `aes`
crate to disable autodetection.