#2228 Fix Dox

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18538 b5f69653-2bf5-0310-8201-b0dafb8e1405
#2183 more work on the cell population writer hierarchy

git-svn-id: https://chaste.cs.ox.ac.uk/svn/chaste/trunk@18540 b5f69653-2bf5-0310-8201-b0dafb8e1405