more space/ and draw/ modules

- 26 errors and 16 doctest fails
- getting there, perpetually

src/draw/thunk.rs

@@ -0,0 +1,16 @@
+use super::*;
+
+pub const fn thunk <T: Screen, F: FnOnce(&mut T)->Usually<XYWH<T::Unit>>> (draw: F) -> Thunk<T, F> {
+    Thunk(draw, std::marker::PhantomData)
+}
+
+/// Because we can't implement [Draw] for `F: FnOnce...` without conflicts.
+pub struct Thunk<T: Screen, F: FnOnce(&mut T)->Usually<XYWH<T::Unit>>>(
+    pub F,
+    std::marker::PhantomData<T>
+);
+impl<T: Screen, F: FnOnce(&mut T)->Usually<XYWH<T::Unit>>> Draw<T> for Thunk<T, F> {
+    fn draw (self, to: &mut T) -> Usually<XYWH<T::Unit>> {
+        (self.0)(to)
+    }
+}