Send binary data
Hi,
first a big thank you for developing and maintaining this library.

quick question:
how would i send binary data, e.g. a file.
i saw by digging around in old issues that there was once a support with an optional flag $isBinary in send method. however you removed that in https://github.com/ratchetphp/Ratchet/commit/237615890d6eb84abc14cc8182c0ccd66fd02b76 with the comment "(should pass message object instead)"

do i understand right, that ive now to manually do something like the following to send binary data:

```php
use Ratchet\RFC6455\Messaging\Frame;
$bin = file_get_contents('file.bin');
$binaryMsg = new Frame($bin, true, Frame::OP_BINARY);
$client->send($binaryMsg);
```

if yes, why is this not documented? in http://socketo.me/docs/migration-3 its only explained how to receive binary messages, not sending them and i found no other source besides that.

Many thanks,
Silver