Support nullable reference types

[ycherkes]

Closes #19

Probably is blocked by the inability to get the information of the root object generic parameters nullability:

NullabilityInfo

Reflection API for Nullability Information
It provides nullability information and context from reflection members:

ParameterInfo
FieldInfo
PropertyInfo
EventInfo

so the following code:

private class Foo<T>
{
    public T Value { get; set; } 
}

var foo = new Foo<string?>{Value = null};

will be dumped to:

var foo = new Foo<string>{ Value = null };