Graphtik

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+ ENH(PLOT): Operation tooltips now show function sources.
+ FIX(site): RTD failing since 5.6.0 due to `sphinxcontrib-spelling` extension
not included n its requirements.
+ FEAT(sphinxext): add :confval:`graphtik_plot_keywords` sphinx-configuration
with a default value that suppresses grafting the title of a netop in the images,
to avoid duplication when :rst:dir:`graphtik:name: <graphtik>` option is given.
+ enh(plot): URL/tooltips are now overridable with node_props
+ enh(sphinxext): permalink plottables with `:name:` option.
+ enh(plot): pan-zoom follows parent container block, on window resize;
reduce zoom mouse speed.

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All previous distributions in *PyPi* since sphinx-extension was added in *v5.3.0*
were missing the new package ``sphinxext`` needed to build sites with
the ``.. graphtik::`` directive.

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--((**BROKEN** because wheel in *PyPi* is missing ``sphinxext`` package))--

+ feat(sol): + :meth:`.Solution.check_if_incomplete()` just to get multi-errors
(not raise them)
+ doc: integrate spellchecking of VSCode IDE & `sphinxcontrib.spelling`.

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--((**BROKEN** because wheel in *PyPi* is missing ``sphinxext`` package))--


Should have been a major bump due to breaking rename of ``Plotter`` class,
but...no clients yet.

+ ENH(plot): plot edges in graphs with `Graphviz`_ ``splines=ortho``.
+ REFACT(plot): rename base class from ``Plotter --> Plottable``;
+ enh(build): add ``[dev]`` distribution extras as an alias to ``[all]``.
doc: referred to the new name from a new term in glossary.
+ enh(site): put RST substitutions in :confval:`rst_epilog` configuration
(instead of importing them from README's tails).
+ doc(quickstart): exemplify ``operation`` as a decorator.

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--((**BROKEN** because wheel in *PyPi* is missing ``sphinxext`` package))--


+ enh(op): use func_name if none given.
+ DOC(quickstart): dynamic plots with sphinxext.

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--((**BROKEN** because wheel in *PyPi* is missing ``sphinxext`` package))--


+ FEAT(PLOT,SITE): Sphinx extension for plotting graph-diagrams as zoomable SVGs (default),
PNGs (with link maps), PDFs, etc.

+ replace pre-plotted diagrams with dynamic ones.

+ deps: sphinx >=2; split (optional) matplolib dependencies from graphviz.

+ test: install and use Sphinx's harness for testing site features & extensions.

+ ENH(op): fail early if 1st argument of `operation` is not a callable.

+ enh(plot): possible to control the name of the graph, in the result DOT-language
(it was stuck to ``'G'`` before).

+ upd(conf): detailed object representations are enabled by new configuration
``debug`` flag (instead of piggybacking on ``logger.DEBUG``).

+ enh(site):

+ links-to-sources resolution function was discarding parent object
if it could not locate the exact position in the sources;

+ TC: launch site building in pytest interpreter, to control visibility of logs & stdout;

+ add index pages, linked from TOCs.