add way to get axes name

[DanPorter]

Currently, when a nexus file is read with hdfmap, the 'axes' and 'signal' paths are automatically generated in the namespace.

However, there is no simple way to recover the name of this group for the purposes of creating plots. The only way to do it at the moment is to use eval:

import hdfmap
f = 'file.nxs'
m = hdfmap.create_nexus_map(f)

x_label = m.eval(m.load_hdf(), '__axes')
y_label = m.eval(m.load_hdf(), '__signal')

There should be a method added to the HdfMap object to recover the path name given a name in the namespace. For example:

x_label = m.get_name('axes')
y_label = m.get_name('signal')

[DanPorter]

if the name is not in the namespace, it should return the same name. A better idea might be:

x_label, y_label = m.generate_axis_labels('axes', 'signal')

[DanPorter]

new in version 1.1, added function generate_ids:

x_label, y_label, detector, expression = m.generate_ids('axes', 'signal', 'IMAGE', 'x-y/y', modify_missing=False)