The binary detection was moved from the parser to the client/server in
[1], in order to allow the user to skip the binary detection for huge
JSON payloads.
```js
socket.binary(false).emit(...);
```
The binary detection is needed in the default parser, because the
payload is encoded with JSON.stringify(), which does not support binary
content (ArrayBuffer, Blob, ...).
But other parsers (like [2] or [3]) do not need this check, so we'll
move the binary detection back here and remove the socket.binary()
method, as this use case is now covered by the ability to provide your
own parser.
Note: the hasBinary method was copied from [4].
[1]: f44256c523
[2]: https://github.com/darrachequesne/socket.io-msgpack-parser
[3]: https://github.com/darrachequesne/socket.io-json-parser
[4]: https://github.com/darrachequesne/has-binary
