Python3 continued

[rapgro]

While build with python 3 and execution of tests:

TypeError: Class advice impossible in Python3. Use the @implementer class decorator instead.

Also, I'll send a pull request to support python3 in all the print commands around in sources.

[rapgro]

see #16 and #25

[rapgro]

The TypeError is a bug in zope:

…
  File "/usr/lib64/python3.9/site-packages/zope/interface/declarations.py", line 706, in implements
    raise TypeError(_ADVICE_ERROR % 'implementer')
TypeError: Class advice impossible in Python3.  Use the @implementer class decorator instead.