Warnings with msgpack 0.5.0

```
/usr/local/lib/python3.6/site-packages/msgpack/__init__.py:47: FutureWarning: use_bin_type option is not specified. Default value of the option will be changed in future version.
return Packer(**kwargs).pack(o)
```

TODO: Need to determine how we handle Unicode strings and how FluentD processes them.

Start with the warning at msgpack/__init__.py:47 and the Packer call shown in the report. Determine how Unicode strings should be handled and how FluentD processes them; done means the behavior is decided and the FutureWarning is addressed accordingly.

Rédigé par le modèle d'indexation à partir du texte de l'issue.