geometry: made Vec2 clamp functions no-return;¹ added fdecl for Quad.

1: To signify that they mutate instead of return a copy.
geometry: moved Vec2 operators to immediately follow struct defs.
geometry: added range-classification functions.
ui: added missing virtual for ProtoContainer and ProtoSlotContainer dtors.

ui::ProtoContainer,
ui::ProtoSlotContainer:
	added missing virtual for dtor.

ui::ProtoContainer: added missing "Implementation" doc-group.
txt::Cursor: optimized col_recalc() when node is singular or col is invalid.
ui::Widget::Base::queue_actions(): check mask_actions, retain clearing render.

ui::Widget::Base::queue_actions():
	check for ui::UpdateActions::mask_actions instead of ~flag_parent;
	if queuing flag_noclear while a clearing render is already queued,
	retain clearing render.
test: removed txt/ops binary and excluded it in .gitignore.

DAMMIT.