Drop support for 3.2

[JelleZijlstra]

Typing recently dropped support for Python 3.2 (python/typing#374) and mypy only supports 3.3 and up. Not sure about pytype and PyCharm. The last release of the 3.2 series was in October 2014 and pip and setuptools don't support it.

Concretely, I propose:

• We stop testing against 3.2 in Travis
• We don't require 3.2 behavior to be supported in new stubs (e.g., functions added in 3.3 don't need a version_info check).
• We don't actively remove existing version checks for 3.2. Removing them is fine as part of a larger refactoring.

#1144 is an example of a PR where supporting 3.2 would complicate the stub needlessly.

[gvanrossum]

Sounds good. I think we should drop 3.2 completely for mypy too.

[gvanrossum]

We debated this and we will do it for mypy and typeshed.

[gvanrossum]

Make it so!

[JelleZijlstra]

I can submit the typeshed PR when I get a chance.