Debug Windows + Python 3.6

[seisman]

Description of proposed changes

Related to #693.

Fixes #

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.

Notes

• You can write /format in the first line of a comment to lint the code automatically

[seisman]

The GMT library gmt.dll exists, but GMT still can't find/load it. Perhaps a broken library?

I'm wondering if it's really worth the debugging time, as we will drop Python 3.6 in the next few months.

[weiji14]

The GMT library gmt.dll exists, but GMT still can't find/load it. Perhaps a broken library?

I'm wondering if it's really worth the debugging time, as we will drop Python 3.6 in the next few months.

What I'm worried about is whether the PyGMT v0.2.1 release works for Python 3.6 users on Windows. I say we leave this PR hanging for now and see if someone reports it (in which case we can tell them to upgrade to Python 3.7 or decide to work on this PR and release PyGMT v0.2.2 as a quickfix).

Oh, and we could also disable the Windows Python 3.6 master CI tests to stop the annoying notifications.

[seisman]

we can tell them to upgrade to Python 3.7

This is what we should do to save us more time.

we could also disable the Windows Python 3.6 master CI tests to stop the annoying notifications.

Yes, please do it.

[seisman]

We dropped Python 3.6 support in #699. This PR is no longer needed.