✨ Add support for Click 8 while keeping compatibility with Click 7

[tiangolo]

✨ Add support for Click 8 while keeping support for Click 7

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[codecov]

Codecov Report

Merging #317 (88075b0) into master (c3a4c72) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master      #317    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          242       252    +10     
  Lines         4508      5287   +779     
==========================================
+ Hits          4508      5287   +779     

Impacted Files	Coverage Δ
..._parameter_types/test_datetime/test_tutorial001.py	100.00% <ø> (ø)
...test_parameter_types/test_enum/test_tutorial001.py	100.00% <ø> (ø)
...est_parameter_types/test_index/test_tutorial001.py	100.00% <ø> (ø)
...st_parameter_types/test_number/test_tutorial001.py	100.00% <ø> (ø)
...st_parameter_types/test_number/test_tutorial002.py	100.00% <ø> (ø)
...test_parameter_types/test_uuid/test_tutorial001.py	100.00% <ø> (ø)
tests/assets/compat_click7_8.py	100.00% <100.00%> (ø)
tests/test_compat/test_option_get_help.py	100.00% <100.00%> (ø)
tests/test_completion/test_completion.py	100.00% <100.00%> (ø)
tests/test_completion/test_completion_install.py	100.00% <100.00%> (ø)
... and 33 more

---

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