Allow plugins to read and write close codes/reasons

[jchampio]

Plugins currently cannot read or write the status code or reason string for close frames. Incoming close frames are completely hidden by the module, and server->close() does not take any code or reason string in its parameter list.

[jchampio]

We also hide incoming pong data, which means plugins can't use ping reflection for anything.

Edit: on second thought, pull this into its own issue: #30