To review

[Mardoxx]

• Make JsonMergePatchDocument<T> [DataContract] serializable

• Remove default(T) for Value in JsonMergePatchValue<T>, make it throw if you try and access an undefined value

• Model Validation
  On ApplyTo() or somehow on deserialization into JsonMergePatchDocument<T>
  The latter would likely be more desirable, and check validation properties on T

• Json Converter
  I have no idea what I'm doing here

• TTo .Apply<TTo>(TTo obj)
  Quickly hacked together, needs research

• Review JsonMergePatchDocument<T>.KnownTypes
  Should [DataMember]s be on the interfaces?

• IImmutableDictionary instead of IReadOnlyDictionary for Members?

• Use custom type instead of KeyValuePair<string, IJsonMergePatchValue> for Members
  Looks a bit weird doing this patchValue.Value.Value
  Or if we have a nullable type, blah.Members(x => x.Key == "NullableType").Value.Value.Value - rather meaningless at first glance!

• Ability to undefine a defined value on JsonMergePatchValue<T>
  Not sure about this

        public bool IsDefined
        {
            get => _isDefined;
            set
            {
                _isDefined = value;

                if (!_isDefined)
                {
                    _value = default(T);
                }
            }
        }

Should this be allowed?

• Explain why it's called RJBM