DOC: Add Technical Reference page for justification codes

[yvonnefroehlich]

Description of proposed changes

Add a Technical Reference page for the GMT justification codes for plot embellishments.

Fixes #4027

Preview
Technical Reference

• https://pygmt-dev--4028.org.readthedocs.build/en/4028/techref/index.html
• https://pygmt-dev--4028.org.readthedocs.build/en/4028/techref/justification_codes.html

Gallery examples and tutorials

• https://pygmt-dev--4028.org.readthedocs.build/en/4028/api/generated/pygmt.Figure.colorbar.html
• https://pygmt-dev--4028.org.readthedocs.build/en/4028/api/generated/pygmt.Figure.inset.html
• https://pygmt-dev--4028.org.readthedocs.build/en/4028/api/generated/pygmt.Figure.text.html
• https://pygmt-dev--4028.org.readthedocs.build/en/4028/gallery/embellishments/colorbar.html
• https://pygmt-dev--4028.org.readthedocs.build/en/4028/gallery/embellishments/scalebar.html
• https://pygmt-dev--4028.org.readthedocs.build/en/4028/tutorials/basics/text.html#adjusting-the-text-label
• https://pygmt-dev--4028.org.readthedocs.build/en/4028/tutorials/basics/text.html#using-the-position-parameter

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 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.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash command is:

• /format: automatically format and lint the code

[seisman]

Please note that justification codes are not only used when plotting embellishments, but also in Figure.text, Figure.meca, Figure.colorbar and more. So, we should have one page focusing on justification codes. We may extend the page and add a separata page for reference/anchor points later.

[yvonnefroehlich]

Please note that justification codes are not only used when plotting embellishments, but also in Figure.text, Figure.meca, Figure.colorbar and more. So, we should have one page focusing on justification codes. We may extend the page and add a separata page for reference/anchor points later.

Hm. I removed the contents related reference/anchor points. However, I am now a bit unsure what to add more to this Technical Reference page. Or do we only want the letters for vertical (TMB) and horizontal (LCR)?

[seisman]

What about adding figures like https://docs.generic-mapping-tools.org/dev/reference/features.html#reference-and-anchor-point-specification or https://docs.gmt-china.org/latest/basis/anchor/?