Exposed embedded key existence in HalResource, added a test to check …

[weierophinney]

Provide a narrative description of what you are trying to accomplish:

• Are you fixing a bug?
  • Detail how the bug is invoked currently.
  • Detail the original, incorrect behavior.
  • Detail the new, expected behavior.
  • Base your feature on the master branch, and submit against that branch.
  • Add a regression test that demonstrates the bug, and proves the fix.
  • Add a CHANGELOG.md entry for the fix.

See zendframework/zend-expressive-hal#52 for details

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Originally posted by @jguittard at zendframework/zend-expressive-hal#53

[alexmerlin]

Closing issue due to being inactive for more than 1 year.