Drop support for end-of-life Pythons

[jdufresne]

Python 2.6 and 3.3 are end-of-life. They are no longer receiving bug fixes, including for security issues. Python 2.6 went EOL on 2013-10-29 and Python 3.3 on 2017-09-29. For additional details on supported Python versions, see:

Active branches: https://devguide.python.org/#status-of-python-branches
End-of-life branches: https://devguide.python.org/devcycle/#end-of-life-branches

Removing support for EOL Pythons will reduce testing and maintenance resources. For example, can begin moving towards a unified Python 2/3 version of pyinotify, reducing massive duplication.

Using pypinfo, here are the download statistic for the last 30 days, showing very low numbers for EOL Pythons.

$ pypinfo --percent --markdown pyinotify pyversion

python_version	percent	download_count
2.7	64.70%	190,361
3.5	28.04%	82,493
3.6	4.68%	13,763
3.4	1.69%	4,973
3.7	0.56%	1,633
2.6	0.27%	790
3.3	0.07%	202
None	0.00%	3
Total		294,218

Changes:

• Can assume functools.reduce always exists
• Can assume ctypes always exists
• Can assume glob.iglob always exists
• Use modern exception handling format (more forward compatible)
• Can use context managers
• Can use octal literal syntax