Add ssl options

Adds the same ssl options provided by `ws` and `tls.connect()`. The options are passed to either `ws` or `https.request` depending on the transport used.

Can be used like so:

```javascript
var opts = {
  key: fs.readFileSync('test/fixtures/client.key'),
  cert: fs.readFileSync('test/fixtures/client.crt'),
  ca: fs.readFileSync('test/fixtures/ca.crt')
};

var socket = new eioc.Socket('https://localhost:3000', opts);
```
If we merge this we can for sure publish the changes, and ideally get them merged upstream all the way to https://github.com/driverdan/node-XMLHttpRequest/