Need to account for both 'datafile' and 'data file'

[tashrifbillah]

We should account for both 'data file' and 'datafile' in Ln 190 and Ln 211 just like:
https://github.com/mhe/pynrrd/blob/master/nrrd/reader.py#L354

[addisonElliott]

:+1 I agree. Personally, I think the easiest option may be to choose one setup data file or datafile (I prefer data file personally) and then stick to it. Thus, have a line like:

if 'datafile' in self.header:
    self.header['data file'] = self.header.pop('datafile')

Then you can assume that there will only be a datafile. Just my initial thoughts.

[tashrifbillah]

Assign: @tashrifbillah