Add documentation labels

[jlaehne]

Description of the change

Added labels to the documentation, particularly for chapter headings, to facilitate referencing from the LumiSpy documentation.

Some minor additions to documentation

Progress of the PR

• Change implemented (can be split into several points),
• update user guide (if appropriate),
• add an changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting changelog entry in the readthedocs doc build of this PR (link in github checks)
• ready for review.

[codecov]

Codecov Report

Base: 80.60% // Head: 80.60% // No change to project coverage 👍

Coverage data is based on head (0828ee7) compared to base (5fd8636).
Patch has no changes to coverable lines.

Additional details and impacted files

@@                 Coverage Diff                 @@
##           RELEASE_next_major    #3085   +/-   ##
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  Coverage               80.60%   80.60%           
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  Files                     176      176           
  Lines                   24476    24476           
  Branches                 5383     5383           
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  Hits                    19729    19729           
  Misses                   3421     3421           
  Partials                 1326     1326           

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[hakonanes]

I recently discovered this nice oneliner

> python -m sphinx.ext.intersphinx https://hyperspy.org/hyperspy-doc/current/objects.inv
py:attribute
	hyperspy._components.eels_cl_edge.EELSCLEdge.effective_angle api/hyperspy._components.eels_cl_edge.html#hyperspy._components.eels_cl_edge.EELSCLEdge.effective_angle
	hyperspy._components.eels_cl_edge.EELSCLEdge.fine_structure_active api/hyperspy._components.eels_cl_edge.html#hyperspy._components.eels_cl_edge.EELSCLEdge.fine_structure_active
# Skip to bottom
	zhou2011                                 [Zhou2011]                              : user_guide/bibliography.html#zhou2011
	zspy-format                              ZSpy - HyperSpy’s Zarr Specification    : user_guide/io.html#zspy-format

which lists all available links in HyperSpy's sphinx documentation. If you combine it with grep, you can search for a specific word in this list

> python -m sphinx.ext.intersphinx https://hyperspy.org/hyperspy-doc/current/objects.inv | grep bibliography
	user_guide/bibliography                  Bibliography                            : user_guide/bibliography.html
	[burdet2013]                             [Burdet2013]                            : user_guide/bibliography.html#burdet2013
# Skip to bottom
	zhou2011                                 [Zhou2011]                              : user_guide/bibliography.html#zhou2011

Thus, some of the added labels are already available for use with Intersphinx, like the one for the "Bibliography". In your reStructuedText, you can use this syntax:

:doc:`bibliography<hyperspy:user_guide/bibliography`

or just

:doc:`hyperspy:user_guide/bibliography`

to use the link from HyperSpy's documentation ("Bibliography").

For later quick reference you can copy the oneliner from the relevant code block in the kikuchipy docs.

[ericpre]

Yes, this is something that we should be using more and we will need to make sure to keep on top of the warnings for broken labels when building the documentation! :)