Basic tls

[mmmries]

Resolves #30

This PR just handles the very basic case where the client has been started with tls: true and the server has tls_required: true settings. I will follow it up with at least 2 more PRs:

• handle cases where the server and client mismatch on requiring TLS
• refactoring the handshake into its own module and passing the entire state to socket_write and socket_close rather than pulling pieces out of the state

I wanted to get this PR opened before tackling either of those other changes since it is already a bit large.

/cc @tallguy-hackett @newellista @film42 @jjcarstens

[mmmries]

💥 Travis ran for 44 seconds to do all test cases