voro++ include path
voro++ installs its headers in PREFIX/include/voro++, so the root CMakeLists.txt must be edited as follow:
find_path(VOROPP_INC "voro++.hh" PATH_SUFFIXES voro++)
(by the way no need to write "PATH_SUFFIXES include/voro++", the "include/" subdir is implicit, checkout the other find_path commands)