Support for plugin before and after, fix ASCII report fails

[gaborbernat]

Resolves #2201 and #2213.

[codecov]

Codecov Report

Merging #2214 (cf6d908) into rewrite (48da366) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           rewrite    #2214   +/-   ##
========================================
  Coverage    99.85%   99.85%           
========================================
  Files          157      157           
  Lines         9017     9058   +41     
  Branches       942      945    +3     
========================================
+ Hits          9004     9045   +41     
  Misses           3        3           
  Partials        10       10           

Flag	Coverage Δ
tests	99.85% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
src/tox/plugin/manager.py	100.00% <100.00%> (ø)
src/tox/plugin/spec.py	100.00% <100.00%> (ø)
src/tox/pytest.py	100.00% <100.00%> (ø)
src/tox/report.py	100.00% <100.00%> (ø)
src/tox/session/cmd/run/single.py	100.00% <100.00%> (ø)
src/tox/util/spinner.py	97.84% <100.00%> (+0.11%)	⬆️
tests/plugin/test_inline.py	100.00% <100.00%> (ø)

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