Add an example for different line styles

[seisman]

Description of proposed changes

Add an example showing lines with different styles:

Preview: https://pygmt-crbc9dplm.vercel.app/gallery/line/linestyles.html

Address #493.

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.

[weiji14]

Looks great! Just had to look up how to plot dashed lines yesterday, and this would have been a super useful reference!

[seisman]

How do I set the milestone and project? Is it for 0.2.x or 0.3.x?

[weiji14]

Go for 0.2.x, there's some bug fixes left to do and we'll most likely need a 0.2.1 release.

[seisman]

Here is a similar plot from matplotlib.

In the matplotlib example, it's much easier to see the line style and the corresponding parameters. I plan to improve our "line styles" example, following the matplotlib one, with the parameters (e.g., 1p,red,-) annotated for lines. Please let me know what you think before I work on the improvements.

[weiji14]

Sounds like a good plan. We probably don't need 16 line examples though, just keep it minimal.

Also, was just looking at the GMT.jl AGU gallery examples at https://www.generic-mapping-tools.org/GMT.jl/latest/gallery/tables/, looks like there's a lot of decorated arrows/curved line examples we can follow.