DOC: filter the correct warning for unique(key, column)

DOC/CLN: clean up indentation and dispatch on numpy version
DOC/BUG: fix overwriting of 'df' variable in doc build
DOC: give deprecation warning about future timeseries broadcasting behavior

DOC/CLN: cleanup
Merge pull request #3815 from cpcloud/doc-build-fix

DOC/BLD: Fix a bunch of doc build warnings that weren't being previously caught
CLN: conform read_clipboard / to_clipboard to new io standards

     removed to io.clipboard (from io.parsers)
Merge pull request #3824 from jreback/clipboard

CLN: conform read_clipboard / to_clipboard to new io standards