Update to NRRD0006

[wraith1995]

Although it is not reflected on the website, nrrd has been updated to allow NRRD0006. If you download the latest version of teem, you will find that you can use NRRD0006 but not NRRD0007. (Try unu head on one file with 6 and one with 7).

We should determine what changes have occurred and update pynrrd accordingly.

[addisonElliott]

You make a good point. Do you have any references on what changes were made between 0005 and 0006? I couldn't find anything online.

Maybe it would be better to wait until Teem publishes a list of differences to save ourselves time of digging through the code to find the new changes.

[wraith1995]

I have no references. We might just have to table this until Teem does something. On the other hand, as far as I can tell from my own usage, the main changes seem to be the addition of new header entries such as "space directions: none (0.002,0) (0,0.002)". It might not be that hard to figure out what new headers have been added and add support for them.