feat: add PD and PID controller implementations (#804)

* feat: add a PID controller implementation

* feat: add small rigid-body utilities + test interpolation test

* fix: make scrolling weaker on macos

* feat: add the option to use the PID controller in the character controller demo.

* feat: add a stateless PD controller

* feat(rapier_testbed): cleanup & support PidController in 2D too

* chore: add comments for the PD and PID controllers

* chore: update changelog

* feat: rename PidErrors to PdErrors which is more accurate

* fix cargo doc

* chore: remove dead code

* chore: make test module non-pub

examples3d/all_examples3.rs

@@ -6,6 +6,8 @@ use wasm_bindgen::prelude::*;
 use rapier_testbed3d::{Testbed, TestbedApp};
 use std::cmp::Ordering;
 
+mod utils;
+
 mod ccd3;
 mod collision_groups3;
 mod compound3;