feat: rename deserialization protocols for clarity, improve usability of error types, and broke up into multiple files. (7.0.0)

[drmohundro]

This pull request covers a variety of improvements.

Renaming XMLIndexerDeserializable protocol and Adding XMLValueDeserialization protocol

I renamed XMLIndexerDeserializable to be XMLObjectDeserialization - its purpose is to deserialize object structures like classes or structs. So, multiple values. Then, there is a new protocol named XMLValueDeserialization - it serves the purpose of both XMLElementDeserializable and XMLAttributeDeserializable. It is only used for custom value deserialization. I hope this will clarify the usage a lot. It makes sense to me anyway!

This should cover the use case at #148.

Usability of Errors

Multiple times when helping people, I'd notice that the nodeIsInvalid error would get thrown, but the error message was just about impossible to determine what was wrong. The code had implemented CustomStringConvertible but everyone was using localizedDescription. Now, errors implement LocalizedError, too, so it is a lot more obvious to see the elements that had caused issues.

Code Reorganization

The code had all been lumped into two Swift files since the beginning. It was unwieldy then, but it has just gotten worse. So I gave in and broke them all out into their own files by type. Much better.

Checklist

• Clean up README (include notes on why naming change, explain error handling a bit more, maybe in FAQs)
• Add CHANGELOG
• Major revision to 7.0.0.
• Covers the discussion up at Improve the deserialization support by making the extension point consistent #148.

[codecov]

Codecov Report

Merging #259 (54e2186) into main (8b594e0) will decrease coverage by 1.28%.
The diff coverage is 68.01%.

@@            Coverage Diff             @@
##             main     #259      +/-   ##
==========================================
- Coverage   66.70%   65.41%   -1.29%     
==========================================
  Files          14       36      +22     
  Lines        1910     1995      +85     
==========================================
+ Hits         1274     1305      +31     
- Misses        636      690      +54     

Impacted Files	Coverage Δ
...e/Deserialization/XMLAttributeDeserializable.swift	0.00% <0.00%> (ø)
...urce/Deserialization/XMLValueDeserialization.swift	0.00% <0.00%> (ø)
Source/XMLHash.swift	82.60% <ø> (+3.34%)	⬆️
...LHashTests/TypeConversionPrimitiveTypesTests.swift	54.34% <0.00%> (ø)
Source/Errors/IndexingError.swift	9.09% <9.09%> (ø)
...rce/Deserialization/XMLElementDeserializable.swift	25.00% <25.00%> (ø)
...rce/Deserialization/XMLObjectDeserialization.swift	25.00% <25.00%> (ø)
Source/Errors/XMLDeserializationError.swift	36.84% <36.84%> (ø)
...eserialization/XMLIndexer+XMLDeserialization.swift	59.74% <45.45%> (ø)
...serializationTypes/Double+XMLDeserialization.swift	50.00% <50.00%> (ø)
... and 19 more

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