Drop support for EOL Python 3.3

[hugovk]

Fixes #357.

[gsnedders]

This won't be merged until pip 11 is near release (assuming pip 11 drops support for Python 3.3, as planned).

[codecov-io]

Codecov Report

Merging #358 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #358   +/-   ##
=======================================
  Coverage   90.76%   90.76%           
=======================================
  Files          50       50           
  Lines        6950     6950           
  Branches     1328     1328           
=======================================
  Hits         6308     6308           
  Misses        483      483           
  Partials      159      159

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[nicktimko]

I'd be curious to just leave the test in there but put it in allowed_failures, then once it actually breaks mark 3.3 as unsupported.

[hugovk]

Python 3.3 has now broken. The master branch now fails on Travis CI for all three Python 3.3 jobs:

Collecting wheel
wheel requires Python '>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*' but the running Python is 3.3.6
----------------------------------------
...Installing setuptools, pip, wheel...done.
Traceback (most recent call last):
  File "/opt/python/3.3.6/lib/python3.3/runpy.py", line 160, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/opt/python/3.3.6/lib/python3.3/runpy.py", line 73, in _run_code
    exec(code, run_globals)
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/virtualenv.py", line 2343, in <module>
    main()
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/virtualenv.py", line 712, in main
    symlink=options.symlink)
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/virtualenv.py", line 947, in create_environment
    download=download,
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/virtualenv.py", line 904, in install_wheel
    call_subprocess(cmd, show_stdout=False, extra_env=env, stdin=SCRIPT)
  File "/home/travis/virtualenv/python3.3.6/lib/python3.3/site-packages/virtualenv.py", line 796, in call_subprocess
    % (cmd_desc, proc.returncode))
OSError: Command /home/travis/build/h.../optional/bin/python - setuptools pip wheel failed with error code 1

https://travis-ci.org/hugovk/html5lib-python/builds/382154525

The newly released pip 10 deprecates 3.3, and it has just been dropped from the codebase: pypa/pip#5423.