support new NeXus method for default/signal/axes/_indices attributes #80
Description
As referenced in nexusformat/definitions#437 (comment), the *_indices attribute(s) are missing from the verysimple example in the introduction. That example uses the nexpy API:
from nexpy.api import nexus
angle = [18.9094, 18.9096, 18.9098, 18.91, 18.9102,
18.9104, 18.9106, 18.9108, 18.911, 18.9112,
18.9114, 18.9116, 18.9118, 18.912, 18.9122]
diode = [1193, 4474, 53220, 274310, 515430, 827880,
1227100, 1434640, 1330280, 1037070, 598720,
316460, 56677, 1000, 1000]
two_theta = nexus.SDS(angle, name="two_theta",
units="degrees",
long_name="two_theta (degrees)")
counts = nexus.SDS(diode, name="counts", long_name="photodiode counts")
data = nexus.NXdata(counts,[two_theta])
data.save("verysimple.nx5")