Replace smart_str by smart_bytes in order to be compatible with python 3

[Yukilas]

The raw_password and salt variables have to be bytes-strings, this is need for the hashlib methods.
For now the code works in python 2 but not in python 3, the current smart_str function does not convert the python 3 unicode string into bytes-string.
With the smart_bytes function, it works for both python 2 and 3.

I bumped the version number to 0.6 so for now we can keep using the current 0.5 version and only use the new one in chuck's python 3 branches.