Add Support for Operators

[Andrei15193]

Currently there is no support for operators. They are not used a lot, however it would be great to have them covered in the documentation tree.

[Andrei15193]

There is a whole bunch of operators that can be overloaded in C# (see: Operator overloading (C# reference)), this will not be targeted in beta1 as operator overloading in generally an edge case and most libraries do not ever overload them.

They will be covered in beta2 as introducing them will cause breaking changes (the DeclarationNodeVisitor will have a few extra abstract methods to cover the operator declaration nodes) which will bump the major version to 2 where operators should be included in version 1 as they are part of the C# language for quite a long time.

As the language progresses new major versions can be introduced as these are language features that could not have been included.