Update README.md

Unindent and add syntax highlighting

Add linux tests against 5.1 and 5.2

…an guarantee (obviously the document contains a primary resource body because it is not an error body). Fix some warnings new as of the 5.2 compiler.

… advantage of key values as functions.

…ip object with no data entry.

…f a now-confusingly-named section in the documentation.

…r documents

…zers

Add some convenience initializers

…pose values.

…APIDocument protocols. Make ResourceObject hashable when its Id is hashable. Make Id's Hashable conformance take its type into consideration since the Id type's primary motivation is to retain differentiation based on the type of thing being identified.

update GitHub Actions workflow to use a test matrix.

…ources

Add CompoundResource.

…se, use ordinal numbers and add a total include count to the message.

…essages.

…t all types are wrong or exactly one type is correct.

…metadata

Add id metadata to relationships.

…ure-errors

Clearer include failure errors

Release/v5

… accuracy.

…ntation

better links documentation paired with a test to ensure documentation accuracy.

fix typo

… compiler up

…ping the compiler up"

This reverts commit 0f79299.

…alias reference that seems to be confusing to the compiler for the thing that typealias references.

Swift 5 4 CI

Add notes about (lack of) Carthage support.

# Conflicts:
#	Package.resolved
#	Package.swift
#	Sources/JSONAPI/Document/Document.swift
#	Sources/JSONAPI/Resource/Resource Object/ResourceObject.swift
#	Tests/JSONAPITests/Document/DocumentDecodingErrorTests.swift
#	Tests/JSONAPITests/Document/DocumentTests.swift
#	Tests/JSONAPITests/Includes/IncludeTests.swift
#	Tests/JSONAPITests/Includes/IncludesDecodingErrorTests.swift
#	Tests/JSONAPITests/Includes/stubs/IncludeStubs.swift