Doxygen documetation comment tidy up for zinc/rendition.hpp.  https://tracker.physiomeproject.org/show_bug.cgi?id=3535
Doxygen documetation comment tidy up for zinc/rendition.hpp.  https://tracker.physiomeproject.org/show_bug.cgi?id=3535

hsorby/zinc,OpenCMISS/zinc,OpenCMISS/zinc,OpenCMISS/zinc,hsorby/zinc,hsorby/zinc,OpenCMISS/zinc,hsorby/zinc