update minimum numpy to 1.10.1

[wholmgren]

I'd like to upgrade the minimum supported numpy version to 1.10.1. This numpy version was released in Oct 2015.

Numpy 1.10 added two features that are useful to us:

1. nan support in assert_allclose
2. scalar support in np.digitize

We've hacked around 1. in the test suite for awhile now, but it would be great to remove the hacked code.

#429 proposes using np.digitize to replace manual binning in the perez function. I could hack around this too, but I'd rather bump the numpy spec.

Any objections to bumping the numpy spec?

[wholmgren]

closed by #429.