Add an "all" granularity to humanize

[MarkKoz]

Pull Request Checklist

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

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

If you have any questions about your code changes or any of the points above, please submit your questions along with the pull request and we will try our best to help!

Description of Changes

Add an "all" granularity to the humanize function. When specified, it internally sets all possible units for the granularity (years, months, weeks, days, hours, minutes, and seconds). This granularity is mutually exclusive with the other granularities; it's not valid to specify it in a list of granularities.

The motivation is that it's more convenient to specify a single string than a list of 7 strings. It will make more sense to use full precision once #997 is merged. Speaking of which, some newly added tests will have to be fixed once #997 is merged and the describe_multi bug is fixed.

Resolve #1014

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (87a1a77) 100.00% compared to head (5b336f2) 100.00%.

:exclamation: Current head 5b336f2 differs from pull request most recent head 71d5233. Consider uploading reports for the commit 71d5233 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #1018   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           10        10           
  Lines         2326      2239   -87     
  Branches       400       440   +40     
=========================================
- Hits          2326      2239   -87     

Files	Coverage Δ
arrow/arrow.py	100.00% <100.00%> (ø)

... and 4 files with indirect coverage changes

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[MarkKoz]

The lint check failure seems to be a problem with CI rather than with my changes.

[systemcatch]

Hmmm lint passes now, looks like it was some kind of setuptools install error that was causing issues.

[jadchaar]

Hi @MarkKoz mind resolving the conflicts in this PR?