DOC: Improve [source] links for C extension types
DOC: Improve [source] links for C extension types

Previously, these would all link to `numpy/core/__init__.py`.
Now the scalar type and `ndarray` link to the files where the `PyTypeObject` is defined.
In future, we should do this for all extension types, probably automatically.

rgommers/numpy,endolith/numpy,anntzer/numpy,mattip/numpy,simongibbons/numpy,numpy/numpy,madphysicist/numpy,grlee77/numpy,pbrod/numpy,simongibbons/numpy,pdebuyl/numpy,madphysicist/numpy,numpy/numpy,mhvk/numpy,jakirkham/numpy,anntzer/numpy,seberg/numpy,madphysicist/numpy,jakirkham/numpy,mhvk/numpy,mattip/numpy,seberg/numpy,jakirkham/numpy,anntzer/numpy,rgommers/numpy,seberg/numpy,mattip/numpy,numpy/numpy,endolith/numpy,madphysicist/numpy,grlee77/numpy,pbrod/numpy,charris/numpy,charris/numpy,pdebuyl/numpy,rgommers/numpy,grlee77/numpy,pbrod/numpy,jakirkham/numpy,pbrod/numpy,charris/numpy,grlee77/numpy,mattip/numpy,endolith/numpy,pbrod/numpy,rgommers/numpy,simongibbons/numpy,jakirkham/numpy,pdebuyl/numpy,simongibbons/numpy,simongibbons/numpy,mhvk/numpy,mhvk/numpy,mhvk/numpy,numpy/numpy,endolith/numpy,pdebuyl/numpy,grlee77/numpy,charris/numpy,madphysicist/numpy,anntzer/numpy,seberg/numpy