0.5.0
-----

The most prominent change of this release is the addition of the
``RestrictedPartHoleDrudge``.  Compared with the ``SpinOneHalfPartHoleDrudge``,
this class is less flexible but can be orders of magnitude faster.  Note that
no backward compatibility is broken by this.  All previous script should still
run fine.  For problems originally written in terms of the unitary group
generators, switching to this new drudge can be really easy.  All these needs
to be done is to remove your own definitions of the unitary group generators,
and use the generator ``e_`` provided by the drudge instead.  For instance, as
in the patch for the `RCCSD example`_.

.. _RCCSD example: https://github.com/tschijnmo/drudge/commit/83f65a690981f7a3c53a93463b58c90d14c9c5ff

With such simple changes, the internals of the evaluations will be switched to
the new scheme and the code will be significantly faster.

In addition of this change, there are also some other revisions,

* A bug in Spark has been circumvented in tensor rewriting.  Thanks to Ethan
  Qiu for pointing this out.

* Tensor definition now allow generic external indices without explicit range.

* A new simplification heuristics is added to simplify summations whose dummy
  is not actually involved in the tensor.

* Add total timing support in ``Stopwatch``.

* Optimize summation discovery based on Einstein summation convention.