mark: Add anchor style to shift marks

[johannes-wolf]

@fenjalien Not sure about the name origin. The idea is to have a style key that shifts the mark origin along its (local) x-axis: 0% tip, 100% base.

• [x] Add documentation
• [x] Add changelog

Fixes #578.

[fenjalien]

Would it be easier to add anchors to the mark function? "tip", "center" and "inset" (or "base") could work

[johannes-wolf]

Would it be easier to add anchors to the mark function? "tip", "center" and "inset" (or "base") could work

As an addition? Because this feature is also useful when placing a mark on a path, e.g., in the center.

[fenjalien]

No, instead of using the origin styling parameter. Anchors would functionally do the same thing but with predefined positions. Given the normal size of marks I don't think you would want such fine control it.

[arkadiuszwojcik]

@fenjalien in such case how it would look like if I would like to use mark center as placement origin?

[johannes-wolf]

mark(..., anchor: "center"), I guess.

[johannes-wolf]

Changed. You can now specify one of the anchors tip, center and base to place the mark at. This also works with marks on paths.

[johannes-wolf]

Can we merge this?