Consider using rustls

[moderation]

By using rustls we could compile dog without requiring OpenSSL and compile using musl.

See https://github.com/osa1/tiny/issues/179 and:

Rustls vs OpenSSL: (link: https://jbp.io/2019/07/01/rustls-vs-openssl-performance.html)

• 15% quicker to send data
• 5% quicker to receive data
• 20-40% quicker to full handshake (client)
• 10% quicker to full handshake (server)
• 30-70% quicker to resume (client)
• 10-20% quicker to resume (server)
• Uses <1/2 as much RAM

[ogham]

I'm not sure if there are any side-effects of switching away from OpenSSL, but I would at least like there to be some way to have pluggable SSL implementations, so users can make the choice for themselves when building it.

[0x5c]

Allowing different SSL crates to be used should be possible with cargo features.