Instead of having to manage the popup menu from your app's build
function, you now just call showPopupMenu() with the menu's position and
it takes care of everything for you.
This solves the problem that the popup menu was trying to mutate the
state of the navigator from within its own initState() function.
Also, remove the "route" argument to RouteBase.build() since it equals
"this" by definition...
Also, remove ModalOverlay, and instead put that logic in the navigator.
Importing the public libraries caused a name conflict with dart:sky because we
assume people will import dart:sky into a namespace, so I've also changed
skysprites to import dart:sky into a namespace.
Also, introduce Colors and Typography to hold the material colors and the
typography declarations. Previously we expected clients of these libraries to
import them into a namespace, but that doesn't play nice with re-exporting them
from material.dart.
Move the animation libraries into src/animation and change importers to use
package:sky/animation.dart. Also, move scheduler.dart into the animation
library so that the animation library can be self-contained.
Turns out many of the functions on BoxConstraints weren't used or had callers
that could easily be updated to other functions. I've added dartdoc to all the
public functions as well as renamed some functions that had similar names but
did different things.