Kotlin code generated for deprecated protocol buffer elements should be marked as deprecated

[wfhartford]

It is possible to mark most protocol buffer elements as deprecated using the deprected option, for example, a message can be deprecated like this:

message Request {
  option deprecated = true;
  string requestContent = 1;
}

When Java code is generated for deprecated elements, they are annotated with @java.lang.Deprecated. I believe that the @kotlin.Deprecated annotation should be applied to deprecated elements in generated Kotlin code.