fixed a bug in statistics
BF: defult z-values are now reosnable. An alternative would be to use Nans.
ENH: better documentation of the contrast function
BF: convert frametimes to array upon design matrix creation
ENH: Change the default for GLM specification: `ols` instead of `ar1`
RF: deprecating unsued code before future removal
BF: fixed a randomly failing test
NF: error if time diff slice axis is time axis

Running time_slice_diff on an array allowed the slice and the time axes
to be the same.  Test that they aren't.
NF: function giving time difference for images

New function that accepts an image as input and returns time series
difference analysis on the image.
WIP: refactor tsdiffana script to select slice axis
WIP: refactoring diagnostics commands into modules
NF: compatiblity routines for older nibabel

Deal with change in nibabel API for getting data object, header and
affine.
NF: add get_unscaled compatibility routine

This allow us to get the unscaled data from an image avoiding the rather
awful read_img_data function that I want to deprecate.
RF: remove yields from test_mask

The test generator makes it more difficult to debug; remove.
BF: get image slope using raw header

I was using the header slope to calculate expected error.  The current
version of nibabel doesn't return the read slope from `get_slope_inter`
as I was assuming here.  Directly read the written header to get the
slope.
RF: use nibcompat module to get unscaled data

mask computation preferred unscaled data, but the routine in nibabel was
broken from recent commits I had done on nibabel, and in any case was
not well designed.  Use a compatibility routine to use the new method in
nibabel if available.
RF: use nibcompat routines for affines, headers

Use nibabel compatibility routines for getting affines and headers from
nibabel images. This avoids running into future warnings when we
deprecate the get_affine, get_header methods.
RF: refuse to load / convert MINC for now

Nibabel can load MINC, but now we need an API to get the axis names for
MINC, otherwise, the axes can be anywhere, but are most likely to be in
the opposite order to the ones the NIfTI needs.  Raise an error until we
have worked out how to do this right.
TST: skip test for non-analyze types for now

In fact it turns out we can't sensibly load the non-analyze types, so
skip this test.
TST: develop tests for tsdiffana command function

Use command function to test the tsdiffana interface.