Expose axis-angle/quaternion conversion functions in transforms package (#486)

Summary:
Fixes https://github.com/facebookresearch/pytorch3d/issues/484

Pull Request resolved: https://github.com/facebookresearch/pytorch3d/pull/486

Reviewed By: bottler

Differential Revision: D25620407

Pulled By: nikhilaravi

fbshipit-source-id: 9a29e4e717aebcca46e46ff5e7bb80a183a92836

pytorch3d/transforms/__init__.py

@@ -2,6 +2,7 @@
 
 from .rotation_conversions import (
     axis_angle_to_matrix,
+    axis_angle_to_quaternion,
     euler_angles_to_matrix,
     matrix_to_euler_angles,
     matrix_to_quaternion,
@@ -10,6 +11,7 @@ from .rotation_conversions import (
     quaternion_invert,
     quaternion_multiply,
     quaternion_raw_multiply,
+    quaternion_to_axis_angle,
     quaternion_to_matrix,
     random_quaternions,
     random_rotation,