I269 citation definitions in body

[alexfargus]

This should address the first issue of #269 - displaying the definition in the body of the document. Creating References section is not covered here.

Changing the styling using as_footnote allows the user to specify whether the target of the citation reference is displayed as a footnote or in the section where it is declared.

The existing behaviour has been kept with as_footnote set to True by default.

[codecov]

Codecov Report

Merging #271 (63cfb8f) into master (a291669) will increase coverage by 0.04%.
The diff coverage is 94.87%.

@@            Coverage Diff             @@
##           master     #271      +/-   ##
==========================================
+ Coverage   73.76%   73.80%   +0.04%     
==========================================
  Files          90       90              
  Lines       14288    14318      +30     
  Branches     1969     1972       +3     
==========================================
+ Hits        10539    10567      +28     
- Misses       3376     3377       +1     
- Partials      373      374       +1     

Flag	Coverage Δ
3.10.0-alpha	73.73% <94.87%> (+0.04%)	⬆️
3.6	73.24% <94.87%> (+0.04%)	⬆️
3.7	73.24% <94.87%> (+0.04%)	⬆️
3.8	73.70% <94.87%> (+0.04%)	⬆️
3.9	73.72% <94.87%> (+0.04%)	⬆️
Linux	73.73% <94.87%> (+0.04%)	⬆️
Windows	73.59% <94.87%> (+0.04%)	⬆️
macOS	73.61% <94.87%> (+0.05%)	⬆️
pypy-3.6	73.27% <94.87%> (+0.04%)	⬆️
pypy-3.7	73.27% <94.87%> (+0.04%)	⬆️
regression-3.10	72.08% <94.87%> (+0.04%)	⬆️
regression-3.6	71.55% <94.87%> (+0.04%)	⬆️
regression-3.7	71.55% <94.87%> (+0.04%)	⬆️
regression-3.8	72.05% <94.87%> (+0.04%)	⬆️
regression-3.9	72.06% <94.87%> (+0.04%)	⬆️
regression-pypy3	71.58% <94.87%> (+0.04%)	⬆️
unit-3.10	47.08% <61.53%> (+0.02%)	⬆️
unit-3.6	45.96% <61.53%> (+0.02%)	⬆️
unit-3.7	45.96% <61.53%> (+0.02%)	⬆️
unit-3.8	47.10% <61.53%> (+0.02%)	⬆️
unit-3.9	47.10% <61.53%> (+0.02%)	⬆️
unit-pypy3	45.99% <61.53%> (+0.02%)	⬆️

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

Impacted Files	Coverage Δ
src/rinoh/reference.py	90.74% <92.59%> (+0.01%)	⬆️
src/rinoh/frontend/rst/nodes.py	85.48% <100.00%> (+0.14%)	⬆️
src/rinoh/stylesheets/matcher.py	100.00% <100.00%> (ø)

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[brechtm]

Thanks for this @alexfargus. Sorry this took so long to review!

I've generalized the code so that as_footnote will also work for plain footnotes. I'll commit those changes soon. I think I'll also replace as_footnote with target (accepts in-place or footnote) so that it's ready to accept additional options (endnote, bibliography?). Suggestions for better labels are welcome :-)