Add rules around variable naming.
Add rules around variable naming.

nickerso/libcellml,nickerso/libcellml,hsorby/libcellml,cellml/libcellml,nickerso/libcellml,hsorby/libcellml,nickerso/libcellml,libcellml/buildbot-testing,hsorby/libcellml,MichaelClerx/libcellml,hsorby/libcellml,libcellml/buildbot-testing,MichaelClerx/libcellml,cellml/libcellml,cellml/libcellml,cellml/libcellml,MichaelClerx/libcellml