Add support for datetime.date

[philippjfr]

While we handle most other datetime types, datetime.date is currently not handled, e.g. when you try the example below you get an error:

hv.Scatter(zip(pd.DatetimeIndex(start='2017-01-01', end='2017-01-04', freq='1d').date, np.linspace(0,1,4)))

[bacalfa]

That'd be great! For Area as well.

hv.Area(zip(pd.DatetimeIndex(start='2017-01-01', end='2017-01-04', freq='1d').date, np.linspace(0,1,4)))

[philippjfr]

Now supported.