Enable Mac and Windows CI on Azure Pipelines

[leouieda]

Description of proposed changes

Delegate the style checks and Mac builds to Azure instead of Travis (for speed).
Deployment still happens on Travis.

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 docstrings or tutorials.

[leouieda]

The library is not being found on Windows because the DLL from conda is gmt.lib and not gmt_w64.lib. We should implement a series of trials for loading the library before giving up. I'll leave that for another PR and merge in with Windows failing now since we don't officially support it yet.