Add context header. Improve query constraint comparison

[cbaker6]

Adds context header option. This requires server level header support, X-Parse-Context (currently missing here: https://github.com/parse-community/parse-server/blob/9ea355b4635226ae4da17c8cc5fb0321e3fdec5e/src/middlewares.js#L38). If added on the server level, will only work with parse-server > 4.5.0.

• Added context header option
• Improved query constraint comparisons
• Improved API header tests
• Added playground context example
• Improve LiveQuery section of readme
• Update Jazzy docs to 0.13.7
• Added changelog
• Prepare for release

[codecov]

Codecov Report

Merging #140 (cd3f9fe) into main (b196fca) will increase coverage by 0.54%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #140      +/-   ##
==========================================
+ Coverage   81.00%   81.54%   +0.54%     
==========================================
  Files          68       68              
  Lines        6374     6384      +10     
==========================================
+ Hits         5163     5206      +43     
+ Misses       1211     1178      -33     

Impacted Files	Coverage Δ
Sources/ParseSwift/API/API.swift	98.18% <100.00%> (+2.14%)	⬆️
Sources/ParseSwift/Types/Query.swift	92.66% <100.00%> (+1.17%)	⬆️
Sources/ParseSwift/Objects/ParseObject.swift	77.54% <0.00%> (+0.53%)	⬆️
Sources/ParseSwift/Coding/AnyEncodable.swift	61.84% <0.00%> (+15.13%)	⬆️

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