Different line styles as example in the Gallery or Cookbook

**Description of the desired feature**

As the possibilities for styling lines has greatly increased over the last couple of months (thank you, Gentlemen) it might be beneficial to document and showcase what can be achieved with the current feature set.

I propose to either expand the [Cookbook chapter 3.13 _Specifying pen attributes_](https://docs.generic-mapping-tools.org/latest/cookbook/features.html#specifying-pen-attributes) which is a bit sparse on the possibilities or add another example in the Gallery.

Your thoughts about this?

**Are you willing to help implement and maintain this feature?** Yes