Bradley Lowekamp

InsightSoftwareConsortium/ITK#3511

InsightSoftwareConsortium/ITK#3496

Refactor Elastix Examples into Sphinx Examples

2

The [elx.cxx](https://github.com/SimpleITK/SimpleITK/blob/master/Examples/elx.cxx) and [tfx.cxx](https://github.com/SimpleITK/SimpleITK/blob/master/Examples/tfx.cxx) examples should be updated to be in separate directory, multiple languages, and integrated into the sphinx documentation.

Update ElastixImageFilter and TransformixImageFilter Doxygen comments

3

The Doxygen comment strings are minimal to non-existent for the above classes. The class level documentation needs improvement.

TODO: the libtbb library still needs to be packaged. The Python tbb package might be able to be used.