Add raw type for defered type decoding

[pkedy]

In certain cases, an application may want to defer deserialization of a data type until it can determine the type of data enclosed in the payload. Similar to Go's json.RawType, raw would be a way of express that raw encoded data is here and preserve the raw encoded bytes. This is different than bytes in that the encoding still contains the actual data types (e.g. object, array, string, primitives) vs being an actual array of bytes.