Add upgrade info

[dbrattli]

• Add upgrade info from v2 to v3
• Loosen choose requirement from list to seq (which works just as well when using lists).
• Format code
• Add Fantomas to GitHub actions.
• Add GitHub example
• Use Ply instead of Taskbuilder (it's faster)
• User FsToolkit.Errorhandling instead of own Result overrides

[codecov[bot]]

Codecov Report

Merging #73 (ccf06a2) into master (020ec1a) will decrease coverage by 5.53%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #73      +/-   ##
==========================================
- Coverage   82.58%   77.05%   -5.54%     
==========================================
  Files           9        8       -1     
  Lines         603      597       -6     
  Branches       30       47      +17     
==========================================
- Hits          498      460      -38     
- Misses         88      104      +16     
- Partials       17       33      +16     

Impacted Files	Coverage Δ
src/Builder.fs	72.22% <ø> (-5.56%)	:arrow_down:
src/Context.fs	78.68% <ø> (-2.46%)	:arrow_down:
src/Error.fs	84.61% <ø> (-15.39%)	:arrow_down:
src/Fetch.fs	80.51% <ø> (-14.29%)	:arrow_down:
src/Logging.fs	69.41% <ø> (-4.71%)	:arrow_down:
src/Handler.fs	76.44% <100.00%> (-3.48%)	:arrow_down:
... and 2 more