Add back support for Python 3.5 and CI tests

[leouieda]

Enable CI runs for 3.5 on Travis and Azure to make it works.

Fixes #92

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to the docstring, gallery, and/or tutorials.