Originally, most of the sources used constructor parameters to set the
various options of the source. Although convenient, it was difficult to
keep track of what each parameter meant. To make the code more clear,
source parameters are now set with accessor functions (e.g.
`SetPointDimensions`). Although this makes code more verbose, it helps
prevent mistakes and makes the changes more resilient to future changes.
This mechanism sets up CMake variables that allow a user to select which
modules/libraries to create. Dependencies will be tracked down to ensure
that all of a module's dependencies are also enabled.
The modules are also arranged into groups.
Groups allow you to set the enable flag for a group of modules at once.
Thus, if you have several modules that are likely to be used together,
you can create a group for them.
This can be handy in converting user-friendly CMake options (such as
`VTKm_ENABLE_RENDERING`) to the modules that enable that by pointing to
the appropriate group.
