Font cannot be overridden yet, but script attributes (language, script
type, direction) and features can be set at all three levels in a
passage. Attributes on the root level act as defaults for the paragraph
and word levels, and paragraph attributes act as defaults for the word
level.
Passage_Delete needs to check if the hierarchy is valid as no text may
have been added, which results in a null pointer for the hierarchy.
Text shaping needs to set language etc every time it resets the buffer.
This causes some problems with linking if libQFgui is linked with
libQFrenderer (which is necessary in the long run), but it seems
everything gets away with it for now (which, tbh, I don't like).
And add a function to process a passage into a set of views with glyphs.
The views can be flowed: they have flow gravity and their sizes set to
contain all the glyphs within each view (nominally, words). Nothing is
tested yet, and font rendering is currently broken completely.
