Custom ID support (string, UUID, etc) and misc bug fixes

[lrstanley]

🚀 Changes proposed by this PR

• BREAKING: renamed Config.AllowClientUUIDs to Config.AllowClientIDs to indicate that it's not specific to UUIDs, but rather any scenario where you want to allow the client to provide their own ID for the CREATE request.
  • Ensure Config.AllowClientIDs actually has an impact. Previously, it only added it to the spec, but didn't add it to the server request handling logic. It's now correctly added to the spec, and the server knows how to handle when a custom ID is provided.
  • WithAllowClientIDs can now be used to toggle this feature on/off on a per-schema basis.
• Added support for ID fields with the underlying types of: string, int, and any other custom type that implements the following interfaces: encoding.TextUnmarshaler, json.Unmarshaler, and encoding.BinaryUnmarshaler (in that order of priority).
  • Switched some tests to include string and UUID-based ID fields.
• Fixed an issue where if an ID field had a custom package type, it may not import the correct package (e.g. uuid.UUID{} could import Google's library, or some other random one that you happen to have locally).
• Improved wording of the id field in the spec, when IDs can be generated on behalf of the CREATE request, when using AllowClientIDs.
• Filter fields in the spec now inherit the format field. For example, id.in on /users now is an array of uuid format type.
• Removed performance suggestion wording from the spec for ?pretty=true.

🔗 Related bug reports/feature requests

• implements feature: Support schema with UUID type id field #69
• closes UUID as ID key for entities #70
• implements feature: Support for String ID fields #76

🧰 Type of change

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that causes existing functionality to not work as expected).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.85%. Comparing base (c0a64c6) to head (1173a13).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #81      +/-   ##
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+ Coverage   68.38%   68.85%   +0.46%     
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  Files          10       10              
  Lines        2442     2456      +14     
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+ Hits         1670     1691      +21     
+ Misses        657      651       -6     
+ Partials      115      114       -1     

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