pytest for wfl command line examples

[bernstei]

Update test_doc_examples.py to correctly handle (at least specially crafted) wfl command line tests.

Note that this initial commit does not include the files needed for the example test.

[bernstei]

I'm going to try to convert the relative paths to absolute paths starting from the location of wfl.__file__, I think.

[bernstei]

I'm going to try to convert the relative paths to absolute paths starting from the location of wfl.__file__, I think.

So I figured out how to do this, but I don't think that for a notebook that's the right approach - I think it makes more sense for the notebook to use its own directory's examples, rather than the one that's linked to the wfl version that import wfl returns. Actually, if wfl is installed from pypi rather than a local repo clone, there may not even be a wfl/examples directory on the system.

[bernstei]

Explanation: I put in a framework for pytest to automatically test docs examples that use the command line. It does it by looking for code blocks that start with !wfl, and replaces them with CliRunner click pytest-compatible python calls. However, I was unable to put in a complete example. The framework is in docs/source/examples.cli.ipynb. Someone else needs to upload the corresponding files to docs/example_files so that command will run and test will pass.