Update docs

Change cols to subset in drop_duplicates

Travis support

Change cols to subset in duplicated and update unit tests

Move test

Fix #6645.  Raises warning on use of cols and update unit tests

Fix docs to use correct pivot_table arguments [#6645, #5505]

Use decorator in all function instead

More old args found in docs

Few more slipped by

Add decorator to to_excel and to_csv

Move to deprecations section