Representation of BSON binary data.
This is necessary because we want to represent Python strings as
the BSON string type. We need to wrap binary data so we can tell
the difference between what should be considered binary data and
what should be considered a string when we encode to BSON.
Raises TypeError if `data` is not an instance of :class:`str`
(:class:`bytes` in python 3) or `subtype` is not an instance of
:class:`int`. Raises ValueError if `subtype` is not in [0, 256).
.. note::
In python 3 instances of Binary with subtype 0 will be decoded
directly to :class:`bytes`.
:Parameters:
- `data`: the binary data to represent
- `subtype` (optional): the `binary subtype
<http://bsonspec.org/#/specification>`_
to use