Adding changelog changelog_v0.3.99-rc.2.rst.
Adding changelog changelog_v0.3.99-rc.2.rst.

cellml/libcellml,hsorby/libcellml,cellml/libcellml,hsorby/libcellml,nickerso/libcellml,cellml/libcellml,nickerso/libcellml,nickerso/libcellml,hsorby/libcellml,hsorby/libcellml,nickerso/libcellml,cellml/libcellml