Now the user doesn't have to supply a visitor capable of visiting all
layers, but instead just the ones they are interested in. Also added
visit_computational_layers() and visit_computational_layers_range()
since those capture a very common use case more concisely than
visit_layers(). That is, users generally want to mess with the
computational layers specifically as those are the stateful layers.
* fix some warnings when running tests
* rever changes in CMakeLists.txt
* update example make use of newly promoted method
* update tests to make use of newly promoted methods
Davis King