Implement multibody joints and the new solver

src/dynamics/joint/impulse_joint/impulse_joint.rs

@@ -0,0 +1,20 @@
+use crate::dynamics::{JointData, JointHandle, RigidBodyHandle};
+use crate::math::{Real, SpacialVector};
+
+#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+#[derive(Clone, Debug, PartialEq)]
+/// A joint attached to two bodies.
+pub struct ImpulseJoint {
+    /// Handle to the first body attached to this joint.
+    pub body1: RigidBodyHandle,
+    /// Handle to the second body attached to this joint.
+    pub body2: RigidBodyHandle,
+
+    pub data: JointData,
+    pub impulses: SpacialVector<Real>,
+
+    // A joint needs to know its handle to simplify its removal.
+    pub(crate) handle: JointHandle,
+    #[cfg(feature = "parallel")]
+    pub(crate) constraint_index: usize,
+}