revert optional mode to relativeTo which selects subsets of font differences; enhance the API to return both the attributes which need changing and the font properties which were different
use new relativeTo API to add any changed font attributes to nodes that accept them (individually), and be careful to track the 'declared font' according to exactly which attributes were set on a parent
adjust to new relativeTo API
add Colorable.attributes to XMApp, so that fractions, roots, etc can pickup the current color
simplify use of _force_font attribute (it isn't needed as often, now)
new layer binds fonts, etc, to better track current font, color
updated test cases for subtle shift in location of color attribute