Update deprecate_kwarg message
DOC: add intersphinx mapping to numpy

There are already some references in the API docs to numpy functions, but the links did not yet work up to now.
Merge pull request #7945 from jorisvandenbossche/depr_message

Update deprecate_kwarg message
Merge pull request #7946 from jorisvandenbossche/intersphinx_numpy

DOC: add intersphinx mapping to numpy
BUG: rolling/expanding_* treamtment of center