Add Sensible APIs to support removing BoringSSL from the rest of the ecosystem

[0xTim]

Related issue apple/swift-nio-ssl#382

APIs:

• Encrypted keys (Encrypted PEM keys #264)
• PKCS#12 support
• PBKDF2 support (New API Proposal: PBKDF2 #98)
• RSA initialisers from ASN.1 (Create RSA keys directly from parsed ASN.1 #269)
• Related expose CNIOBoringSSL swift-nio-ssl#484

[Lukasa]

Thanks for filing this Tim. Can I ask that we collaborate on trying to populate a list of what those items are? If people feel like making suggestions in the thread, I'll update the issue with a bulleted list.

[0xTim]

I'll add them as I see them