Fixed in operator with null values

When second argument to "in" operator is null, evaluator was throwing an argument error. This release includes a fix, which correctly returns false in the case where second argument evaluates to null.

Added string comparisons

This is a tiny release to include the string-based comparisons contributed by @FrederikLynggaard .

Thanks for the contribution.

Version 1.1.9 - Added netstandard2.1 support.

Merge pull request #20 from yavuztor/dev

Added netstandard2.1.

Version 1.1.8

Minor updates. See release notes.