feature request: addition of AES-CTR (and optionally, SIV-AES)

[kwvg]

Description

AES-GCM is not adequate for some applications with stream ciphers bearing greater practicality. CTR mode also comes with parallelism potential.

[mcarrickscott]

Sorry, missed this. In fact some legacy modes of operation, like CTR, are already (sort of) supported. For example see core::AES_encrypt in aes.cpp

[kwvg]

I'd be really grateful if it can be fleshed out with explicit API calls as (at least personally), I'd prefer AES_CTR_encrypt over AES_encrypt (could be GCM?).

Would make code review much more easier. I would love to contribute but the possibility of borking something is high enough to act as discouragement.