Clean up legacy Sphinx hacks and resolve longstanding warnings.

Support use of NISTtheDocs2Death to put documentation on
https://pages.nist.gov/fipy.

Previous configuration went to great lengths to "see" things
outside documentation directory, which is not the intended
design of sphinx. Using autodoc instead of autosummary simplifies
things considerably.

* Guard examples against running on import

    Examples should not run when building docs

* Change paths so Sphinx builds canonically in documentation/ dir

* Account for NaN deviation in plots

    Single points have no standard deviation? Used to work, but no more

* Move index files to Sphinx source directory

* Move Sphinx content into Sphinx source directory

* Rename AbstractCommWrapper to CommWrapper

* Move figures into Sphinx source directory

* Remove py:attr reference to target `self.vars[0]`

* Fix name of `array_like`

* Fix deprecations

* Fix targets in doc strings

* Fix typos

* Add base classes to `__all__` for documentation cross-links

* Fix name of base class

* Stop indexing explicit examples

    Some examples now appear in two locations
    [TODO: Sorting that out is misery for another day]
    - in the explicit list of examples
    - in the examples API documentation
    Loud warnings if we try to index both, so only index the API variant.

* Simplify API toctree

* Clear up root of examples documentation

* Fix tutorial documentation toctree

* Add mock imports for solvers that probably aren't installed

* Update intersphinx mappings

* Stop generating autosummary for examples

    Examples are referred to explicitly and in API.
    Don't need autosummary, too?

* Fix broken links

* Remove references to obsolete classes

* Make module name legal

* Fix typo

* Fix target type

* Make labels unique

* Link to examples in API documentation

    Removes duplicate entries

* Explicitly denote "single" index entries

    The
    ["shorthand" notation](https://www.sphinx-doc.org/en/master/usage/restructuredtext/directives.html#directive-index)
    raises lots of spurious warnings about
    `Explicit markup ends without a blank line; unexpected unindent.`

* Fix path to included file

* Ignore modules file

* Specify attribute path

* Fix markup of combined attribute

* Fix duplicate footnotes

* Update instructions for building documentation

    Much changes when using Sphinx's canonical `make html`.

* Remove build_docs command from setup

* Stop hiding api docs

* Fix crosslink to updating instructions

* Fix broken links

* Fully specify inherited object to document

* Mute Mayavi documentation issues

* Fix target reference for factory method

* Move ElPhF documentation from TeX to module docstring

* Change target type for Python standard types

    :keyword:`dict` links to
    https://docs.python.org/3/reference/expressions.html#dict
    but :keyword:`list` doesn't link to
    https://docs.python.org/3/reference/expressions.html#list-displays
    ?

    :class:`dict`, :class:`list`, and :class:`tuple` are more
    appropriate, anyway.

* Don't nitpick references to files and the like

* Remove arcane `__all__.extend`

    Rely on public imports for public API

* Distinguish pyAMG LU from SciPy LU

* Fix references to objects no longer in Brobdingnagian `__all__`

* Document generic solver classes

* Activate de-coupled binary phase field example

* Fix LaTeX glitches of long standing

* Migrate machinery from for turning .rst into .tex inputs

    Not sure this belongs in conf.py,
    but don't know where else it belongs

* Move LaTeX formatting into a .sty file

* Move documentation into separated layout

    Separate source and build directories is what
    [Sphinx seems to prefer](https://www.sphinx-doc.org/en/master/tutorial/getting-started.html#creating-the-
   documentation-layout).

* Wrap lines and have apidoc process examples

* Point workflow to new location of docs

* Update action inputs

* Move requirements.txt into docs folder

    This is where sphinx-action (and, now, NISTtheDocs2Death)
    are looking for it.

* Create directory for generated output

* Wrap commands with parentheses

* Use line-continuing backslashes

* Require fipy in order to build fipy docs

* Look for packages one level up

* Remove obsolete action input

* Switch API documentation to autosummary

* Change imports to avoid Sphinx bug

    Importing part of a package within itself causes
    [autosummary weirdities](https://github.com/sphinx-doc/sphinx/issues/8963)

* Move docstring to class from __init__

    Shouldn't be necessary, because `autoclass_content = "both"` is set...

* Update version

* Install git

* Bump version of ntd2d

* Skip numpy 1.25 dispatch functions

* Silence Sphinx autosummary errors

    Documented some items, hid others.

    `autosummary <https://www.sphinx-doc.org/en/master/usage/extensions/autosummary.html>`_
    and/or `autodoc <https://www.sphinx-doc.org/en/master/usage/extensions/autodoc.html>`_
    really didn't like "`matplotlibViewer/matplotlibViewer`".
    Possibly related to https://github.com/sphinx-doc/sphinx/issues/11362

 ?

* Add module docstrings

* Add pip requirements

* Stop building docs (badly) on Azure

* Install git with apt-packages

* Make workdirectory a git safe.directory

* Add badges for GH Actions

* Remove Codacy badge

    Codacy is no longer free

* Fix conda-forge badge

* Switch docs pre-requisites to conda

* Update badges on static index.html

* Install self with conda from parent directory
* Fix reST

* Remove depsy badge

    Project hasn't been maintained in five years and badge is broken
    (because it's only available as an http:// link in an https:// page?)

* Add mock imports for petsc4py, mpi4py, and mayavi

* Update searchbox to be consistent with basic theme

* Add more mock imports

* Add intersphinx mapping for mayavi

* Stop using "is" and "is not" to compare with literals

    Addresses #891

* Fix spelling

* Fix renaming missed in 819fbfa

* Switch from mamba to conda in Py2.7

* Ensure logging is configured

* Fix unicode module contents for Py2.7

* Fix typo

Co-authored-by: Trevor Keller <trevor.keller@nist.gov>

* Add brief explanation of each chunk of examples

* Make multiline pre-build-command "chomping"

* Convert rst to tex with make

* Generate PDF

* Remove file conversion from configuration

* Make Makefile more makey

* Collapse examples into a single chapter

Co-authored-by: Trevor Keller <trevor.keller@nist.gov>