feat(isAlpha, isAlphanumeric): add Esperanto (eo) locale

[RobinvanderVliet]

I have added Esperanto (eo) support to the methods isAlpha and isAlphanumeric. Esperanto is not a language of a specific country, that is why there is no country code.

Checklist

• [x] PR contains only changes related; no stray files, etc.
• [x] README updated (where applicable)
• [x] Tests written (where applicable)
• [x] References provided in PR (where applicable)

References

• https://en.wikipedia.org/wiki/Esperanto_orthography
• https://www.akademio-de-esperanto.org/fundamento/gramatiko_angla.html
• https://bertilow.com/pmeg/skribo_elparolo/skribo/literoj.html
• https://lernu.net/esperanto#:~:text=Here%20is%20the%20Esperanto%20alphabet.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (4197b86) to head (45b0d99).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2285   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          107       107           
  Lines         2449      2449           
  Branches       619       619           
=========================================
  Hits          2449      2449           

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[RobinvanderVliet]

I have merged master in my branch.