DOC: Added 'top' buttons to top level object separators in documentation.
Merge pull request #1021 from rhattersley/v1.6.x-conflicts

Fixes from v1.6.x
Merge pull request #1017 from pelson/top_buttons_on_horiz_rule

DOC: Added 'top' buttons to top level object separators in documentation.
Add iris.util.intersection()