implement std::error::Error for aead::Error

[s97712]

aead::Error doesn't implement std::error::Error, then can't work with some error library such as fail, anyhow
consider implement std::error::Error for aead::Error?

[tarcieri]

That was added here:

RustCrypto/traits#63

...unfortunately I don't have access to release the aead crate

[newpavlov]

This issue is fixed in aead v0.3.

[jhpratt]

@tarcieri Is it possible to add a std feature to the various reverse dependencies? I'm using aes_gcm_siv, and am currently having to pull in aead as a direct dependency just to enable the feature.