Provide a complete set of swift keywords, quote their usage

[TheMadBug]

fixes #118 Handle keyword "private" - I've extended this to all swift keywords.

Note that my solution did involve removing the old replaceKeywords method which would append Property, and instead escapes keywords with the "`" character.

e.g. {"class": 123} used to generate a variable called classProperty where now it generates a variable called class but all referencs to it are escaped with quotes. I'm not sure if this is going to cause issues with existing users.

Lastly I moved the detection of keywords to the bottom of fixVariableName rather than the top, so if any other processing converts the variable to a reserved word, e.g. " private".trim() -> "private" it's caught.

[coveralls]

Pull Request Test Coverage Report for Build 381

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 0.0%

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Totals
Change from base Build 365:	0.0%
Covered Lines:	0
Relevant Lines:	0

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💛 - Coveralls

[codecov[bot]]

Codecov Report

Merging #122 into dev will decrease coverage by 0.08%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #122      +/-   ##
==========================================
- Coverage   98.96%   98.88%   -0.09%     
==========================================
  Files          16       16              
  Lines         873      808      -65     
==========================================
- Hits          864      799      -65     
  Misses          9        9              

Impacted Files	Coverage Δ
Core/Generator/NameGenerator.swift	100.00% <100.00%> (ø)
...iftyJSONAcceleratorTests/ModelGeneratorTests.swift	99.47% <100.00%> (-0.05%)	:arrow_down:
...AcceleratorTests/MultipleModelGeneratorTests.swift	96.00% <0.00%> (-0.35%)	:arrow_down:
Core/Helpers/JSONHelper.swift	97.14% <0.00%> (-0.05%)	:arrow_down:
Core/Generator/ModalGenerator.swift	100.00% <0.00%> (ø)
Core/Generator/FileGeneratorExtension.swift	100.00% <0.00%> (ø)
Core/Generator/MultipleModelGenerator.swift	100.00% <0.00%> (ø)
SwiftyJSONAcceleratorTests/StringTests.swift	100.00% <0.00%> (ø)
... and 2 more

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