DOC: sparse: add the function 'find' to the module-level docstring
MAINT: update pip wheelhouse for installs

Astropy wheelhouse no longer being used by astropy; switch to Rackspace
container.
ENH: cluster: rewrite and optimize hierarchy in Cython
Merge pull request #3860 from WarrenWeckesser/add-find-to-mod-doc

DOC: sparse: add the function 'find' to the module-level docstring
Merge pull request #3866 from matthew-brett/update-wheelhouse

MAINT: update pip wheelhouse for installs
Merge pull request #3792 from richardtsai/rewrite_hierarchy

ENH: cluster: rewrite hierarchy in Cython