Support both http: and https: ports simultaneously

[jbemmel]

For my application some clients/flows need to use https:, and some things can be handled over plain http. I tried instantiating 2 SocketCluster objects, but it will only allow me to instantiate one (singleton)

Ideally, in the SocketCluster options, one would be able to specify a list of ports, with protocol options for each

[jondubois]

It's better to explicitly create a new socket if the first URL fails. It's clearer if this is handled explicitly in your own application logic.