refs #320
Update NXxbase.nxdl.xml

refs #317
fixes #316
Merge branch 'development' of https://github.com/nexusformat/definitions into development
restore entry for NXvalidate (Java GUI)

Somehow, NXvalidate was removed from the documentation but still referenced in the h5py example.  Since NXvalidate is still in the code repository (<code>/applications/NXvalidate), it should be represented in the manual.
more explanation

additional content from the ``nxvalidate.1`` man page file from NXvalidate
re-insert

inadvertently omitted from #303
remove "link" attributes

fixes #334
Merge branch 'master' into development
Merge branch 'master' into development
emphasize early on that NeXus is used for both raw and processed data
reduce displayed figure sizes here, remove unnecessary "The"
take a longer view
h5py has a new documentation URL
Focus at this point on the basic building blocks: groups, fields, attributes, links
emphasize the HDF5 implementation details over the legacy HDF4 and XML details