Find a work around for lack of support for String.Normalize()

[kal]

In the constructor for BaseLiteralNode, the code was enforcing Unicode normalization form C by calling the String.Normalize() method. However, this method is not available dnxcore50 so currently the call to normalize the string is commented out.

It would be nice to find a workaround for this if possible.

[kal]

This also affects the IsValidUriRefEncoding method in RdfXmlSpecsHelper (though in this case it is the lack of the String.IsNormalized() method.

[kal]

Also RDFXMLParser line 1026 and 1518

[kal]

...and DomBasedEventGenerator in dotNetRDF.IO.Xml

[kal]

There is a NuGet package implementing string normalization for PCL: https://github.com/Turo-NET/UnicodeNormalization

The source is under MIT license so it is possible to either contribute a .NET Core build to that project or else to fork and build a .NET Core version for our own use.