move to www.numpy.org
Merge pull request #2872 from sandrotosi/master-numpy.org

DOC: point links to www.numpy.org
fix array interface documentation links
Merge pull request #2873 from sandrotosi/master-numpy.org

DOC: fix array interface documentation links
DOC: Add missing minus sign

The int64 data type allows numbers from -9223372036854775808 to
9223372036854775807. The minus sign was missing.
Merge pull request #2874 from certik/fixdoc

DOC: Add missing minus sign