Add option for SSL-enabled virtualhosts

[JacobDB]

Somewhat related to #49, it'd be awesome if we could add support for SSL virtualhosts. Now that Service Workers are so big in web development, it's key to be able to test with SSL.

This would work by setting an --ssl_cert=/path/to/certificate.crt and/or --ssl_key=/path/to/key.key flag that would add an additional virtualhost to the file. Setting one of these parameters and not the other would default the other to the same path, swapping the file extension (i.e. if only -ssl_cert=/path/to/certificate.crt was passed, ssl_key would be assumed to be /path/to/certificate.key).

Ideally this script could also generate the keys themselves, but I think that may be a bit out of scope.