Method 2: support python 2 and python 3 by requiring clients to pass 8-bit string parameters.

[tacitus-aedifex]

this is an alternative way to support both python 3 and python 2. this version doesn't do any string conversion, instead the programmer is required to pass strings of 8-bit values. i added a decorator that throws a ValueError exception if the programmer passes the wrong string type to the pysodium functions. this also cleans up the test cases so that they all pass strings of 8-bit values to the pysodium functions.

[tacitus-aedifex]

whoops, forgot to change python2 to just python in the test script...fixed.

[stef]

i would reverse the checks in the decorator, instead of checking for one wrong type to be passed, i'd raise an error if not the correct type is passed. i.e. for py2

if not isinstance(arg,str): raise ValueError(...)