Publish functions ModifyValue and WithUpdate.

[fujiwara]

Hi. Thank you for a great library!

jsondiff works perfectly to create diff by ignoring some elements. See also fujiwara/lambroll#281

So I'm considering using jsondiff to ignore some elements of json structures.

In this PR https://github.com/fujiwara/lambroll/pull/283/files, I try to ignore specified elements in json before creating parameters for deployment.

I want to use jsondiff.ModifyValue and WithUpdate from outside this package.

[codecov]

Codecov Report

Base: 69.54% // Head: 69.54% // No change to project coverage 👍

Coverage data is based on head (eb9aae8) compared to base (3689e59).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #23   +/-   ##
=======================================
  Coverage   69.54%   69.54%           
=======================================
  Files           2        2           
  Lines         197      197           
=======================================
  Hits          137      137           
  Misses         42       42           
  Partials       18       18           

Impacted Files	Coverage Δ
diff.go	72.46% <100.00%> (ø)

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[aereal]

Thank you for contributing and using this library!