Feature Request: Serialize IPAddress

Created by: EmperorArthur

Currently compilation fails if ArdunioJson attempts to serialize an IPAddress object.

On the surface, this makes sense because it is not something which can be directly converted to JSON. However, Serial.print(..) explicitly works, so it catches users off gaurd.

Code to convert IPAddress to a string, which can be serialized.

out = String(address[0]) + "." + String(address[1]) + "." + String(address[2]) + "." + String(address[3])