Rework special docstring in pyopenms

[jpfeuffer]

Currently it is: Documentation available here: $hugeUnreadableLink

Here in create_cpp_extension.py

Should be rst link syntax. Plus I vote for storing the pxd file and maybe also line for every ResolvedClass. https://github.com/OpenMS/autowrap/blob/ecc05b7dfb5dd155ee43b9617e05d0fd78790458/autowrap/DeclResolver.py#L165

Then we can put a link to the GitHub source code as well. See the corresponding autowrap issue.