Currently it's not practical to read a stream of BSON documents (sometimes called a "document sequence") using a bson.Decoder. However, it is possible to write a stream of BSON documents using bson.Encoder, so Decoder should support the inverse functionality.

Definition of done:

• Change the bson.NewBSONDocumentReader (renamed to NewValueReader) input to an io.Reader instead of []byte.
• Make sure the stream reading behavior works with Extended JSON as well.
• (Optional) Consider following the pattern of the Go JSON decoder More function.
• Update the internal valueReader type to support reading a stream of documents instead of just one.
• Add an example of how to read a stream of documents.