Separate version specific scripts p2

[gyermolenko]

In continuation to #287

With this PR all 4 example scripts with metaclass usage have two versions.

What I found out is that:

• blackboard outputs are random and can't be tested as is
• flyweight almost certainly can be refined ( see also )

Future plans/ideas:

• add diff compare of __py2/__py3 files to CI so they be updated together
• add tox config to make linting/tests with different py versions easier

[codecov-io]

Codecov Report

Merging #288 into master will decrease coverage by 4.91%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #288      +/-   ##
==========================================
- Coverage   66.85%   61.94%   -4.92%     
==========================================
  Files          58       59       +1     
  Lines        2091     2181      +90     
==========================================
- Hits         1398     1351      -47     
- Misses        693      830     +137

Impacted Files	Coverage Δ
patterns/other/blackboard__py2.py	0% <ø> (ø)
patterns/structural/flyweight__py2.py	0% <0%> (ø)
patterns/other/blackboard__py3.py	0% <0%> (ø)
patterns/structural/flyweight__py3.py	0% <0%> (ø)

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