Allow CanTherm to save multiple job outputs to chem.inp.

The resulting chem.inp will not be a complete Chemkin file, but will contain
snippets that can be easily moved into Chemkin files.
Change all Cython attributes marked readonly to public.

This allows us to compile RMG-Py again with the latest version of Cython
(0.19). Cython 0.17.x and 0.18.x still do not work because of another issue.
Despite the change, you should probably still treat these attributes as read-
only.