Rigid-body-motion

---------------------------

Bug fixes & improvements
~~~~~~~~~~~~~~~~~~~~~~~~

* Fixed ``transform_coordinates`` failing when spatial dimension is first
axis of array.
* Fixed ``transform_linear_velocity`` and ``transform_angular_velocity``
failing when reference frame or moving frame is transformed across only
static transforms.
* Added ``allow_static`` parameter to ``lookup_twist``,
``lookup_angular_velocity`` and ``lookup_linear_velocity`` to return zero
velocity and no timestamps across only static transforms.

---------------------------

New features
~~~~~~~~~~~~

* New ``lookup_linear_velocity`` and ``lookup_angular_velocity`` top-level
methods.
* New ``render_tree`` top-level method for printing out a graphical
representation of a reference frame tree.
* ``lookup_twist`` now accepts a ``mode`` parameter to specify the mode for
angular velocity calculation.

Bug fixes & improvements
~~~~~~~~~~~~~~~~~~~~~~~~

* Fixed a bug where estimated angular velocity was all NaN when orientation
contained NaNs.

--------------------------

New features
~~~~~~~~~~~~

* Reference frames with timestamps now accept the ``discrete`` parameter,
allowing for transformations to be fixed from their timestamp into the
future.
* ``rbm`` accessor for DataArrays implementing ``qinterp`` and ``qinv``
methods.
* New ``best_fit_rotation`` and ``qinterp`` top-level methods.

Bug fixes & improvements
~~~~~~~~~~~~~~~~~~~~~~~~

* Refactor of internal timestamp matching mechanism defining a clear priority
for target timestamps. This can result in slight changes of timestamps
and arrays returned by transformations but will generally produce more
accurate results.
* Added ``mode`` and ``outlier_thresh`` arguments to
``estimate_angular_velocity``.
* Fixed issues with ``iterative_closest_point``.

--------------------------

New features
~~~~~~~~~~~~

* New ``estimate_linear_velocity`` and ``estimate_angular_velocity`` top-level
methods.
* New ``qmul`` top-level method for multiplying quaternions.

-------------------------

Improvements
~~~~~~~~~~~~

* Use SQUAD instead of linear interpolation for quaternions.

----------------------------

Bug fixes
~~~~~~~~~

* Fix transformations failing for DataArrays with non-numeric coords.