Render API documentation on the website

We should render the API on the website, including bindings:

Language | Status | Where | How
--- | --- | --- | ---
C++ | done | https://api.precice.org/cpp | Doxygen
C | done | https://api.precice.org/c |Doxygen
Fortran (C implementation) | done | https://api.precice.org/fortran | Doxygen as C functions, Fortran module not available
Fortran Module | [missing](https://github.com/precice/fortran-module/issues/32) | | [Doxygen](https://www.doxygen.nl/manual/docblocks.html#fortranblocks)
Python | done | https://api.precice.org/python | via sphinx (autodoc for cython)
Rust | [barebone](https://github.com/precice/rust-bindings/pull/12) | https://api.precice.org/rust forwards to [docs.rs](https://docs.rs/precice/latest/precice/struct.Participant.html) | via cargo rustdoc
Julia | [missing](https://github.com/precice/PreCICE.jl/issues/79) | | [documenter.jl](https://documenter.juliadocs.org/stable/man/guide/)
Matlab | missing | | ?

_edit: updated the table_