Better Binary support
Following msg18676, I propose to change the Binary management and to use: bytearray for Python2 and bytes for Python3. This solution has many advantages:
- almost the same type on both version
- correct type for Python3 (could not be achieve with Python2 because bytes is str and thus json try to dump it even with binary values)
The drawback is that bytearray is mutable which is not very good but it can be enforced by convention.