DOC: Update docs to use consistently x * and y *

[michaelgrund]

Description of proposed changes

Currently in the docs the versions

• x direction
• y direction
• x-direction
• y-direction
• x-dimension
• y-dimension
• x axis
• y axis
• x-axis
• y-axis

are used. The versions without '-' are used most frequently. This PR makes the docs consistent.

Preview:

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.

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[yvonnefroehlich]

Yeah, this is currently a bit inconsistent in the docs and examples.🙃. Actually, I believe we also use the upper case versions partly, e.g., https://www.pygmt.org/dev/api/generated/pygmt.Figure.text.html.

[seisman]

• https://www.mathworks.com/help/matlab/ref/xlabel.html
• https://matplotlib.org/stable/api/_as_gen/matplotlib.axes.Axes.set_xlabel.html

Perhaps "x-axis" is more common?

[michaelgrund]

• https://www.mathworks.com/help/matlab/ref/xlabel.html

  • https://matplotlib.org/stable/api/_as_gen/matplotlib.axes.Axes.set_xlabel.html

Perhaps "x-axis" is more common?

Means we should always use the hyphen version, so x-axis, x-direction, x-dimension etc. or differentiate between the individual terms?