Proposal to add six new HMAC SHA-2 PRF identifiers for PBKDF2

Hi,

Attached is my proposal to add six new HMAC SHA-2 pseudorandom
function (PRF) identifiers for PBKDF2, a commonly used method for
password-based encryption.

Let's use this as a concrete example for adding new code points for an
existing mechanism. Hopefully we can come up with a streamlined
process for such requests.

Thanks,
Wan-Teh Chang