Dynamic Humanize and describe_multi Bug Fix

[anishnya]

Pull Request Checklist

Thank you for taking the time to improve Arrow! Before submitting your pull request, please check all appropriate boxes:

• [ ] 🧪 Added tests for changed code.
• [ ] 🛠️ All tests pass when run locally (run tox or make test to find out!).
• [ ] 🧹 All linting checks pass when run locally (run tox -e lint or make lint to find out!).
• [ ] 📚 Updated documentation for changed code.
• [ ] ⏩ Code is up-to-date with the master branch.

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Description of Changes

Closes #996 and #973. I'll add the documentation for dynamic humanize after we make sure we like the approach we have here. Also, I'm linking #983 since I had to make some change to describe_multi that will be useful info for the locale implementation guide.

[codecov[bot]]

Codecov Report

Merging #997 (995ee01) into master (baebfff) will not change coverage. The diff coverage is 100.00%.

:exclamation: Current head 995ee01 differs from pull request most recent head e3a7f93. Consider uploading reports for the commit e3a7f93 to get more accurate results

@@            Coverage Diff            @@
##            master      #997   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines         2223      2164   -59     
  Branches       350       345    -5     
=========================================
- Hits          2223      2164   -59     

Impacted Files	Coverage Δ
arrow/arrow.py	100.00% <100.00%> (ø)
arrow/locales.py	100.00% <100.00%> (ø)
arrow/factory.py	100.00% <0.00%> (ø)

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