Fixes for parsing escaped / quoted strings

[StefH]

#307

[codecov]

Codecov Report

Merging #326 into master will increase coverage by 0.17%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #326      +/-   ##
==========================================
+ Coverage   88.56%   88.74%   +0.17%     
==========================================
  Files          46       47       +1     
  Lines        4531     4540       +9     
==========================================
+ Hits         4013     4029      +16     
+ Misses        518      511       -7     

Impacted Files	Coverage Δ
...ystem.Linq.Dynamic.Core/Parser/ExpressionParser.cs	88.58% <100.00%> (+0.40%)	⬆️
...em.Linq.Dynamic.Core/Parser/SpracheStringParser.cs	100.00% <100.00%> (ø)

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