Drop EOL Python 2.6 and 3.3

[hugovk]

Fixes https://github.com/kennethreitz/records/issues/141.

Python 2.6 and 3.3 are EOL and no longer receiving security updates (or any updates) from the Python core team.

They're also little used.

Here's the pip installs for records from PyPI for last month:

python_version	percent	download_count
2.7	52.47%	1,720
3.6	30.54%	1,001
3.5	8.66%	284
3.4	8.30%	272
2.6	0.03%	1

Source: pypinfo --start-date -56 --end-date -26 --percent --pip --markdown records pyversion

This PR also 3.6 to the classifiers, and 3.4 and 3.5 to Travis CI, and updates to use automatic formatters, new in 2.7.

[vlcinsky]

@hugovk could you rebase, text (run tox and see, it fails under python2.7 due to utf-8 chars in setup.py which are already fixed in master)?

If not, I could fix the extraneous metadata for python3.3 on my own.

Do you consider the format fix important?

[hugovk]

Rebased!

The format fix isn't hugely important.

[vlcinsky]

Thanks!