Align with RFC 8018 (obsoletes RFC 2898)

[sthagen]

As RFC 8018 obsoleted RFC 2898 after being 16 years in "operation" - I propose to ensure, the library also implements the PBKDF2 key derivation function described in the RFC successor.

My inspection of the two RFC's (section 5.2) did not expose any notable difference but in the appendix B.1 as expected, the former single example (default for this implementation as I understood):

An example pseudorandom function for PBKDF2 (Section 5.2) is HMAC-
SHA-1.

is augmented in the new edition (RFC 8018) to:

Examples of pseudorandom function for PBKDF2 (Section 5.2) include
HMAC with SHA-1, SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, and
SHA-512/256. Applications may employ other schemes as well.

So, it might be worth to revisit the default chosen.

The reporter considers the target of this issue as an improvement 😸