TST: Copied existing tests for BusinessDay for CustomBusinessDay to test that
the CustomBusinessDay class can be used as a drop-in replacement of the
BusinessDay class. Note that this doesn't yet test any of the additional
functionality provided by CustomBusinessDay and only tests that it functions
equivalently to BusinessDay.
BUG: Added missing objects identified by the tests added in e0f8b3d.
TST: Added tests for the holidays and weekmask functionality of the
CustomBusinessDay class.
DOC: Added notes on the CustomBusinessDay class to the release notes as well as
the TimeSeries documentation.