adding links to first references of the vocabulary items

[sanbrock]

If base class reference is the same as the first reference, do not duplicate the information and have the same link listed twice

[phyy-nx]

Discussion from Code Camp:

• Remove dependency on pynxtools, by adding the new function as new code either alongside or inside dev_tools/docs/nxdl.py
• Instead of a verbose link to the dependecy (e.g. <NXxbase/entry>, use ... and a pop up tool tip that says "This field extends NXxbase/entry" with a link to NXxbase/entry.
• The above may require a new Sphinx subpage dependency. That's ok. Example: https://sphinx-hoverxref.readthedocs.io/en/latest/

[sanbrock]

Code Camp suggestions are implemented, the new format is
definition: (required) NX_CHAR …🔗
with tootip of override: NXxbase/entry/definition
Also the external dependency pynxtools is removed and the code is integrated.

[sanbrock]

Override linking has been modified, and collapsible documentation/enumeration has been added according to the CC discussion.

[PeterC-DLS]

Could you rebase this change off the newly refactored method in nxdl_utils.py? This will remove the dependencies on h5py and click

[sanbrock]

yes, sure

[domna]

When I build the python package, it has a version of 0.0.0. Perhaps set it to something other than the default.

@PeterC-DLS You should now get a correct version when building the package

[phyy-nx]

Superseded by #1303