py3: traceback.pyi: added format_stack - #125

You can use https://www.python.org/dev/peps/pep-0484/#version-and-platform-checking

So it's legal to write something like

if sys.version_info[0] >= (3, 4):
    def foo(x: Bar) -> Baz: ...

Note that mypy doesn't fully support this yet (the current version will assume that foo() is always there, also you can't put two different signatures into the if and the else).

So it's like adding a comment # Python 3.4 only, but it'll also get semantical meaning at some point.

Could you also update the 2.7 version? Agreed with Matthias on how to add version-specific features.

Merging this now, but please see previous comments -- ping?

Hello!

Sorry for the delay; I planned to get this done on the (last) weekend, but things got in the way (as they have a tendency to do).

Shall I submit a new PR or update this?

Please update this one -- you can just add more commits. I'll squash them when I merge.