Add SSL/TLS and headers injection support

Two additional features:
 * SSL support, with automatic detection
 * Websocket handshake headers injection support (very simple)

By default URLs starting with `wss://` will default to port 443. User can force SSL by adding `:ssl => true` (i.e. as with `:host => 'some.host.org'` and `:port => 8080`).

Header injection works by providing a key-value hash in `:headers` param.

Example:
```
WebSocket::EventMachine::Client.connect(
    :uri => 'wss://ssl.someservice.org',
    :headers => {'Secret-Key' => 'random'}
)
```