refs #28, makes existing structure almost NeXus compliant, still needs a hard link from /entry/instrument/detector/data to /entry/data/data
need support software interface to create NDF5 hard links from specifications in an XML file
refs #28, transform "performance" into a NeXus NXcollection group
refs #28, changes indicated by Ulrik
fixes #29
Merge pull request #30 from prjemian/master

refs #28 but not fully NeXus compliant