The overnight doxygen build gave warnings like:
```
.../Linear_cell_complex/doc/Linear_cell_complex/Linear_cell_complex.txt:108: warning: unable to resolve link to '::import_from_triangulation_3' for \link command
.../Linear_cell_complex/doc/Linear_cell_complex/Linear_cell_complex.txt:109: warning: unable to resolve link to '::import_from_polyhedron_3' for \link command
.../Linear_cell_complex/doc/Linear_cell_complex/Linear_cell_complex.txt:112: warning: unable to resolve link to '::import_from_plane_graph' for \link command
```
when building against the doxygen master due to the fact that doxygen was a bit more stringent
Added the namespace to the links
(also tested against doxygen 1.9.6 after the changes).
albert-github
8efdbff899