Libertinus: Implement more ligatures

[KrasnayaPloshchad]

The following diagraphs and trigraphs marked in blue need to be implement ligatures. Actually it’s not hard work, the new glyph can be done by derivating existed glyphs.

Note: the second section is showing discretionary ligatures, the _ij_ ligature in Linux Libertine G is available with Dutch locale.

[KrasnayaPloshchad]

Seen from Wikimedia Commons, I think all of them can become ligature.

[moyogo]

I'd recommend breaking down those ligatures into components so they can be formed dynamically with contextual substitutions, for example f.beforetophook, f.beforeascender, f.beforesoftdot, etc.

[khaledhosny]

Agree with @moyogo (in case some one volunteers to do this, I’m not). Also long s+s needs to be kerned better, no ligature needed. The c+k and c+h ligatures does not make much sense other than in blackletter, so should actually be dropped.

[KrasnayaPloshchad]

@moyogo I agree with you, I found EB Garamond 12 produced ligatures in this way.

[skef]

Ligature support is now uniform across the main Serif faces. Which is not to say that all of the above have been added.