pkcs8: password protected private key support

[GentleVincent]

Hello,
I learned that PKCS#8 is a standard for storing and transferring private key information. The wrapped key can either be clear or encrypted, I can't find any information in crate PKCS8 about how to set a password protected PKCS8 wrapped key, does the crate PKCS8 has any module, function or trait to set a password to protect the PKCS8 wrapped key? Thanks!

[tarcieri]

Per the rustdoc:

https://docs.rs/pkcs8/0.3.3/pkcs8/#supported-algorithms

Encrypted private keys are presently unsupported.

[tarcieri]

Closing in favor of #263