Fix default for pen parameter in API documentation

[yvonnefroehlich]

Description of proposed changes

This PR aims to fix the default for the pen parameter in the API documentation.

Default pen: width = default, color = black, style = solid
also occurs in the upstream GMT documentation (e.g. https://docs.generic-mapping-tools.org/dev/coast.html#i). If the change to
Default pen: width = 0.25p, color = black, style = solid
is correct, I can try to open an corresponding PR in the next days.

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• 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 wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.

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[yvonnefroehlich]

This PR aims to fix the default for the pen parameter in the API documentation.

Default pen: width = default, color = black, style = solid also occurs in the upstream GMT documentation (e.g. https://docs.generic-mapping-tools.org/dev/coast.html#i). If the change to Default pen: width = 0.25p, color = black, style = solid is correct, I can try to open an corresponding PR.

I am unsure about making this change in the upstream GMT documentation. I realized that it is possible to use default for the pen attribute width. However, from a user perspective, I feel a more descriptive argument would be nice, i. e. 0.25p (or at least thinnest), even user can look this up at https://docs.generic-mapping-tools.org/6.4/cookbook/features.html#wpen-attrib.
Ping @GenericMappingTools/pygmt-maintainers for thoughts on this, please.

[seisman]

This PR aims to fix the default for the pen parameter in the API documentation.
Default pen: width = default, color = black, style = solid also occurs in the upstream GMT documentation (e.g. https://docs.generic-mapping-tools.org/dev/coast.html#i). If the change to Default pen: width = 0.25p, color = black, style = solid is correct, I can try to open an corresponding PR.

I am unsure about making this change in the upstream GMT documentation. I realized that it is possible to use default for the pen attribute width. However, from a user perspective, I feel a more descriptive argument would be nice, i. e. 0.25p (or at least thinnest), even user can look this up at https://docs.generic-mapping-tools.org/6.4/cookbook/features.html#wpen-attrib. Ping @GenericMappingTools/pygmt-maintainers for thoughts on this, please.

The upstream GMT maintainers also agree that we should use 0.25p rather than default when talking about the default pen width. See GenericMappingTools/gmt#4006 and GenericMappingTools/gmt#3993.

[yvonnefroehlich]

This PR aims to fix the default for the pen parameter in the API documentation.
Default pen: width = default, color = black, style = solid also occurs in the upstream GMT documentation (e.g. https://docs.generic-mapping-tools.org/dev/coast.html#i). If the change to Default pen: width = 0.25p, color = black, style = solid is correct, I can try to open an corresponding PR.

I am unsure about making this change in the upstream GMT documentation. I realized that it is possible to use default for the pen attribute width. However, from a user perspective, I feel a more descriptive argument would be nice, i. e. 0.25p (or at least thinnest), even user can look this up at https://docs.generic-mapping-tools.org/6.4/cookbook/features.html#wpen-attrib. Ping @GenericMappingTools/pygmt-maintainers for thoughts on this, please.

The upstream GMT maintainers also agree that we should use 0.25p rather than default when talking about the default pen width. See GenericMappingTools/gmt#4006 and GenericMappingTools/gmt#3993.

Thanks @seisman for your response and the links to the upstream GMT PRs. I opened a PR to make this change in the upstream GMT documentation.