Test with two versions of Sphinx
Test with two versions of Sphinx

I do not consider compatibility with old versions to be essential but I
believe we are so it would be good to test it to make sure that we don't
accidentally drift away.

We can then consciously remove older versions as we choose. Two reasons
for not overly valuing backwards compatibility are that Sphinx is a
documentation generator and therefore not a core code path for most
projects and so they can afford to update more easily, and also we use
internal Sphinx APIs which are more likely to change and so be hard to
stay compatible with multiple versions.

Here we use the Travis environment functionality to test two versions of
Sphinx as recommended here:

    http://docs.travis-ci.com/user/languages/python/#Testing-Against-Multiple-Versions-of-Dependencies-(e.g.-Django-or-Flask)

AnthonyTruchet/breathe,AnthonyTruchet/breathe,AnthonyTruchet/breathe,RR2DO2/breathe,kirbyfan64/breathe,AnthonyTruchet/breathe,kirbyfan64/breathe,kirbyfan64/breathe,kirbyfan64/breathe,RR2DO2/breathe