clarify that https can be used within 'signalk-http'
clarify that current spec only covers 'v1' within discovery schema
clarify that endpoint locations are fixed in v1
clarify how to deal with IPv6 endpoints
clarify that insecure and secure endpoints cannot co-exist on a v1 server (ie. you can't have both http and https unless one is on IPv4 and the other on IPv6
Improve documentation:
closes #482 and closes #485