add some verification against MATLAB output

Add a new test which checks that the output from the Python code matches
that of MATLAB to within machine precision.
fix for not including Yscale output in dtwavexfm2

This is a cautionary tale for testing. Actually *verifying* against
MATLAB lead to the discovery that the Yscale returned by dtwavexfm2 was
utterly wrong. The scale image was repeatedly written to Yscale[0] and
the remaining levels were None.
add colifilt verification test
workaround for Python 2/3 incompatibility with npz

The npz format uses pickle to store objects. The pickle format is
incompatible between PYthon 2 and 3 due to Unicode encoding issues. We
work around this by ensuring that we only store plain ol'arrays in the
npz file. It's mucky, but compatible.
Merge pull request #19 from rjw57/additional-verif

add some verification against MATLAB output