BVH animation loading / retargeting (#25)

This PR adds support for BVH animation files, with a custom animation
player and retargeting solution for our Blender Rigify-based skeletal
meshes.

---------

Co-authored-by: Brooks Palin <brookspalin710@gmail.com>

studio-bvh/src/joint_cursor.rs

@@ -0,0 +1,42 @@
+use crate::Bvh;
+use mint::Vector3;
+
+#[derive(Debug)]
+pub struct JointCursor<'a> {
+    bvh: &'a mut Bvh,
+    index: usize,
+}
+
+impl<'a> JointCursor<'a> {
+    #[inline]
+    pub const fn index(&self) -> usize {
+        self.index
+    }
+
+    #[inline]
+    pub fn push_joints(&mut self) -> PushJointsChain<'a> {
+        PushJointsChain { cursor: self }
+    }
+}
+
+#[derive(Debug)]
+pub struct PushJointsChain<'a> {
+    cursor: &'a mut JointCursor<'a>,
+}
+
+impl<'a> PushJointsChain<'a> {
+    pub fn push_joint<B: AsRef<[u8]>, V: Into<Vector3<f32>>>(
+        &mut self,
+        name: B,
+        offset: V,
+    ) -> Self {
+        todo!()
+    }
+}
+
+impl<'a> From<&'a mut Bvh> for JointCursor<'a> {
+    #[inline]
+    fn from(bvh: &'a mut Bvh) -> Self {
+        Self { bvh, index: 0 }
+    }
+}