add new type: :stacked_absolute

[JoshAusHessen]

Adds the new type stacked_absolute for bar charts.
It accepts absolute values rather than deltas and can deal with negative values.
#95

[mindok]

Thanks @JoshAusHessen - it looks pretty straightforward. Are you happy to add a gallery entry to demonstrate how it is different to a stacked bar chart in the docs?

[JoshAusHessen]

Are you happy to add a gallery entry to demonstrate how it is different to a stacked bar chart in the docs?

Yes, of course. I wanted to wait if there is interest in the changes at all.
I will try to find some time next week for the gallery as well as the interactive samples project.

[JoshAusHessen]

missclick 😅

[JoshAusHessen]

@mindok I hope I got everything to add to the gallery.
It looks like this:

Not the nicest, but I'm unsure how to change the text size and so on.