Refactor glyph info lookup

[schriftgestalt]

I just had a look at the way the glyph info is generated (from looking at Jans pull request #778).

There are two (or three) function that do ligature lookup (in _construct_production_name, _construct_category and soon _construct_script). I would recommend to put the fallback into _lookup_attributes (or make a new one like _lookup_attributes_with_fallback). So that it returns the needed attributes for all names that it can recognize. (or rename _lookup_attributes to _lookup_attributes_data and make a new _lookup_attributes)

I can have a look when the pull request is merged.

[madig]

This reminds me, have you posted your algorithm for (sub)category determination anywhere? The code in glyphsLib continues to scare me.