…truction

…riate units

In particular, 'now' needs time-like units, and 'today' needs
date-like units.

Now it always goes to the more precise unit.

…ange

Here I've realized that default 'microsecond' units isn't very good,
and would like to make a default 'generic' unit instead.

This allows integers to convert into timedeltas without binding
to a default unit, so that later when it's combined with another
data type it adopts that type instead of overriding it haphazardly.
This makes things generally more intuitive.

… is given

…function

This cleans up the implementation of arange a lot, and makes the
promotion rules behave consistently.

The complexity of the operations desired for business days is such
that expressing it as a unit in the datetime doesn't fit naturally.
Instead, an API operating on day-based datetimes appears to be
a superior approach.

…ction

…algorithm

…thon

… reductions

The default NPY_DATETIME type was still in microseconds, because it
wasn't using the NPY_DATETIME_DEFAULTUNIT macro as it should have been.
The reduction functions in ufuncs didn't respect the metadata appropriately.

…bject

…usdaydef

… busdaydef

…s day API

… on Chuck's feedback

…pecifier

One fairly major improvement is that parsing with kind and a size now
makes sure there isn't any garbage after the size.

…1867)

MW: I've removed the asbytes part and changed 'S5' to 'S0' from
    Derek's original commit.

…rations