Changes

Build the documentation files with CMake. (#1240)

* Refactor the Jenkinsfile a bit.

* Build the documentation files with CMake.

* Add a CMake Find module for Sphinx.

  - This should have been added by previous commits but was overlooked.

* Remove requirement for Doxygen's 'dot' component.

  - Unfortunately, this does not seem to be available (or accessible?) on
    the docker image used for Linux build on Jenkins.

  - In any case, I think the documentation should be generated just fine
    with CMake since the Makefiles based generation was working fine on
    the same setup.