Fix escape characters parsing

[StefH]

#163

[codecov]

Codecov Report

Merging #264 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #264      +/-   ##
==========================================
+ Coverage    96.5%   96.52%   +0.01%     
==========================================
  Files          41       41              
  Lines        7213     7242      +29     
==========================================
+ Hits         6961     6990      +29     
  Misses        252      252

Impacted Files	Coverage Δ
...c/System.Linq.Dynamic.Core/Tokenizer/TextParser.cs	100% <100%> (ø)	⬆️
...ystem.Linq.Dynamic.Core/Parser/ExpressionParser.cs	98.65% <100%> (ø)	⬆️
src/System.Linq.Dynamic.Core/Parser/TypeHelper.cs	100% <100%> (ø)	⬆️
.../System.Linq.Dynamic.Core/Parser/KeywordsHelper.cs	100% <0%> (ø)	⬆️
src/System.Linq.Dynamic.Core/Parser/Constants.cs	100% <0%> (ø)	⬆️

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