Support vertical writings

[GrimPixel]

Is your feature request related to a problem? Please describe.

In Mongolian writing system, texts are written top-to-bottom, left-to-right; In traditional Japanese, it is top-to-bottom, right-to-left. Both are actively used.

Describe the solution you'd like

Support vertical writings. It is called “writing-mode” in CSS.

[jzohrab]

Could users use a custom style for that? https://jzohrab.github.io/lute-manual/usage/themes/custom-styles.html#vertical-text-for-japanese

[GrimPixel]

Great to know that. Default values can be set for writing systems not horizontal-lr: https://www.omniglot.com/writing/direction.htm