Bump version to 0.12.0, update `CHANGELOG.md`

[codecov[bot]]

Codecov Report

Merging #210 (0355e5c) into master (8a07649) will increase coverage by 0.08%. The diff coverage is 95.65%.

@@            Coverage Diff             @@
##           master     #210      +/-   ##
==========================================
+ Coverage   73.71%   73.80%   +0.08%     
==========================================
  Files          43       43              
  Lines        2359     2355       -4     
==========================================
- Hits         1739     1738       -1     
+ Misses        620      617       -3     

Impacted Files	Coverage Δ
Sources/XMLCoder/Auxiliaries/Box/KeyedBox.swift	100.00% <ø> (ø)
Sources/XMLCoder/Auxiliaries/XMLStackParser.swift	93.54% <ø> (-0.14%)	:arrow_down:
Sources/XMLCoder/Encoder/DynamicNodeEncoding.swift	50.00% <0.00%> (ø)
Sources/XMLCoder/Decoder/XMLDecoder.swift	76.64% <100.00%> (+0.34%)	:arrow_up:
...es/XMLCoder/Decoder/XMLDecoderImplementation.swift	67.55% <100.00%> (+0.09%)	:arrow_up:
...s/XMLCoder/Decoder/XMLKeyedDecodingContainer.swift	81.81% <100.00%> (+1.15%)	:arrow_up:
...XMLCoder/Decoder/XMLUnkeyedDecodingContainer.swift	36.29% <100.00%> (ø)
Sources/XMLCoder/Encoder/XMLEncoder.swift	87.50% <100.00%> (-0.08%)	:arrow_down:
...es/XMLCoder/Encoder/XMLEncoderImplementation.swift	76.57% <100.00%> (ø)

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[github-actions[bot]]

	Fails
:no_entry_sign:	Error deserializing SwiftLint JSON response (): dataCorrupted(Swift.DecodingError.Context(codingPath: [], debugDescription: "The given data was not valid JSON.", underlyingError: Optional(Error Domain=NSCocoaErrorDomain Code=3840 "The data is not in the correct format.")))

Generated by :no_entry_sign: Danger Swift against 34b2194a485d320385f3341f350a120a157c22b7