Provide examples for serializer and virtual

[steffengates]

The text included below is all that is mentioned about virtual and serializer. These are incredibly useful features - but their use is kind of a mystery. Could the read me be expanded to show a small example of each?

"virtual is a configuration option which allows us to define closures with custom serialization behavior (json,xml)

serializer unlike virtual which will create completely new property, this configuration options allows us to customize serialization output for existing property"

[mskec]

You can find examples in test directory of this repo. I know there should be example in readme, but you can use unit test examples for now.