TODO - Refactoring

easier way to define magic tuneable constants
- and maybe to recalculate fixedish things if they change?

Map layer

fixed precision math
- more careful geom types, with negative/positive cases
- also bounds?
- cant get rid of the ccw intersection check... different answer in some cases that looks bad
maybe also the time to split into different lane types? what's similar/not between them?
- graph querying?
- rendering (and other UI/editor interactions)?
- sim state?
- Sidewalk, Parking, Street

rename Car->Vehicle?
spawning is convoluted
- popdat trip -> Scenario SpawnTrip -> pick ped speed and make spawner's TripSpec -> create trip and schedule a Command -> last minute rewriting when executing the command
more precise car FSM by putting scheduler pointer into carstate

probably use f32, not f64 everywhere... but after Pt2D becomes fixed size
undo the y inversion hacks at last!
ezgui passes EventCtx and DrawCtx with appropriate things exposed.
- maybe move glyph ownership out of canvas entirely. dont need RefCell.
  - need to pass around a NonDrawCtx very uniformly first for this to work
- canvas owning text-drawing is maybe a bit weird, at least API-wise
- hide stuff inside the ctx's? canvas and prerender shouldnt even be known outside of crate
generic World with quadtree should have actions on objects
loading screen
- FileWithProgress should go directly into Timer
  - need to understand lifetimes
- cleanup abstutil Timer stuff generally