Initial support for sphinx.ext.graphviz

[rappdw]

resolves #299

Support for directives from sphinx.ext.graphviz

There is a TODO that should be resolved, but I'm unsure how to proceed

1. see line #640 in nodes.py: should the graphviz :classes: property factor into image styling, and if so, how?

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #300 (3d12ddb) into master (488e6dd) will decrease coverage by 28.93%.
The diff coverage is 36.36%.

@@             Coverage Diff             @@
##           master     #300       +/-   ##
===========================================
- Coverage   76.03%   47.10%   -28.94%     
===========================================
  Files          92       92               
  Lines       14397    14408       +11     
  Branches     1986     1986               
===========================================
- Hits        10947     6787     -4160     
- Misses       3031     7462     +4431     
+ Partials      419      159      -260     

Flag	Coverage Δ
3.10.0-alpha	47.09% <36.36%> (-28.91%)	⬇️
3.6	45.95% <36.36%> (-29.57%)	⬇️
3.7	45.95% <36.36%> (-29.57%)	⬇️
3.8	47.09% <36.36%> (-28.85%)	⬇️
3.9	47.09% <36.36%> (-28.86%)	⬇️
Linux	47.06% <36.36%> (-28.90%)	⬇️
Windows	47.06% <36.36%> (-28.76%)	⬇️
macOS	47.06% <36.36%> (-28.77%)	⬇️
pypy-3.7	45.97% <36.36%> (-29.59%)	⬇️
regression-3.10	?
regression-3.6	?
regression-3.7	?
regression-3.8	?
regression-3.9	?
regression-pypy3	?
unit-3.10	47.09% <36.36%> (-0.01%)	⬇️
unit-3.6	45.95% <36.36%> (-0.01%)	⬇️
unit-3.7	45.95% <36.36%> (-0.01%)	⬇️
unit-3.8	47.09% <36.36%> (-0.01%)	⬇️
unit-3.9	47.09% <36.36%> (-0.01%)	⬇️
unit-pypy3	45.97% <36.36%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/rinoh/frontend/rst/nodes.py	52.07% <36.36%> (-33.22%)	⬇️
src/rinoh/frontend/commonmark/__init__.py	0.00% <0.00%> (-100.00%)	⬇️
src/rinoh/backend/pdf/xobject/png.py	14.46% <0.00%> (-79.88%)	⬇️
src/rinoh/flowable.py	33.84% <0.00%> (-61.57%)	⬇️
src/rinoh/table.py	35.03% <0.00%> (-58.71%)	⬇️
src/rinoh/backend/pdf/__init__.py	30.67% <0.00%> (-58.41%)	⬇️
src/rinoh/font/opentype/truetype.py	41.93% <0.00%> (-58.07%)	⬇️
src/rinoh/backend/pdf/util.py	27.27% <0.00%> (-57.58%)	⬇️
src/rinoh/paragraph.py	35.13% <0.00%> (-57.41%)	⬇️
src/rinoh/font/opentype/cff.py	28.69% <0.00%> (-57.40%)	⬇️
... and 50 more

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[brechtm]

Thanks! Don't worry about the failing CI jobs. I'll address your questions, fix some things and merge.

[brechtm]

I merged your work and made some tweaks in 82348c2. Cheers!