Make code Python 3 compatible

In `test.py` discovered an apparent bug in `np.rec.fromrecords` (https://github.com/numpy/numpy/issues/4201).  There is currently no test of `pprint()` or `pformat()`, but by-hand run showed unexpected output for unicode strings.  This would apply for Py2 and Py3.
```
In [1]: run -i test.py
/data/baffin/tom/git/Ska.Numpy/Ska/Numpy/__init__.py

In [2]: import Ska.Numpy

In [3]: Ska.Numpy.__file__
Out[3]: '/data/baffin/tom/git/Ska.Numpy/Ska/Numpy/__init__.py'

In [4]: Ska.Numpy.pprint(ra)
icol         fcol         scol                                
1            3.4          s1                                  
-1           4.3          hey                                 
1            3.4          there                               
100          3.0          string                              
10           8.4          col sdfas                           

In [5]: ra.dtype
Out[5]: dtype([('icol', '<i8'), ('fcol', '<f8'), ('scol', '<U36')])
```