Cantera website - increase doxylink use in Sphinx documentation

[ischoegl]

Problem description

We keep getting inquiries on the UG about where different parts of Cantera functions are implemented. For this, it would be beneficial to increase the use of doxylinks in the documentation (as an aside, this was one item I attempted to resolve in Cantera/cantera#1548 for the YAML API documentation).

As a somewhat related example, there is a reference for InterfaceRate->coverage-dependencies that could benefit from reformatting (although it may be preferable to link to the corresponding C++ documentation and doxygen @cite the reference there).