The `CellMeasures` and `MeshQuality` filters had constructors that took the
metric that the filter should generate. However, this is different than the
iterface of the rest of the filters. To make the interface more consistent,
these filters now have a default (no argument) constructor, and the metric
to compute is selected via a method. This makes it more clear what is being
done.
In addition, the documentation for these two classes is updated.
The original design of the filter base class required several specialized
base classes to control what information was pulled from the input
`DataSet` and provided to the derived class. Since the filter base class was
redesigned, the derived classes all get a `DataSet` and pull their own
information from it. Thus, most specialized filter base classes became
unnecessary and removed.
The one substantial exception was the `FilterField`. This filter base class
managed input and output arrays. This was kept separate from the base
`Filter` because not all filters need the ability to select this
information.
That said, this separation has not been particularly helpful. There are
several other features of `Filter` that does not apply to all subclasses.
Furthermore, there are several derived filters that are using `FilterField`
merely to pick a single part, like selecting a coordinate system, and
ignoring the rest of the abilities.
Thus, it makes more sense to deprecate `FilterField` and have these classes
inherit directly from `Filter`.
This is a start of moving the VTK-m User's Guide into the VTK-m source.
This is only the start of the process. There are several goals of this
work.
1. Integrate the documentation into the source code better to better
keep the code up to date.
2. Move the documentation over to Sphinx so that it can be posted online
and be more easily linked.
3. Incoporate Doxygen into the guide to keep the documentation
consistent.
4. Build the user guide examples as part of the VTK-m CI to catch
compatibility changes quickly.
