Parse delimited from test

Hi, I need to parse multiple messages from one file. In Google protocol buffers I used [parseDelimetedFrom](https://developers.google.com/protocol-buffers/docs/reference/java/com/google/protobuf/AbstractParser#parseDelimitedFrom(java.io.InputStream)). This is my attempt to implement same method wire-way.
The only method i came up with was add constructor with Sink to WireOutput and use it in [writeRawByte](https://github.com/drakelord/wire/blob/master/wire-runtime/src/main/java/com/squareup/wire/WireOutput.java#L218-224).