Disable ligatures for literal text
Implement field lists using LabeledFlowable
GroupingElement: CustomElement returning its children as GroupedFlowables
Framed: border and background for flowables

- introduce ShapeStyle
- inherit from LineStyle (rename its attributes to avoid name clash)
- fix Polygon rendering (fill)
- fix color stroking
- splits across containers (but needs more work)
Rename indent_left/right to margin_left/right