Create a new font features tag attribute.
You can use this attribute to select OpenType font features like small-caps, alternative glyphs, ligatures, etc. for fonts that support them.
features |
a string with OpenType font features, with the syntax of the [CSS font-feature-settings property](
https://www.w3.org/TR/css-fonts-4/ |
the newly allocated `PangoAttribute`, which should be freed with [[email protected]] |