add advanced option for each sphinx builder
add advanced option for each sphinx builder

TODO: connect this bool to the creation of a target
TODO: if testing is enabled, all external links should be checked

InsightSoftwareConsortium/ITKExamples,InsightSoftwareConsortium/ITKExamples,InsightSoftwareConsortium/ITKExamples,InsightSoftwareConsortium/ITKExamples,InsightSoftwareConsortium/ITKExamples