Merge pull request #2610 from square/jwilson.0110.deprecate_simple_xml

Deprecate our SimpleXmlConverterFactory

retrofit-converters/simplexml/README.md

 Simple XML Converter
 ====================
 
+Deprecated – Please switch to the JAXB Converter
+------------------------------------------------
+
+The Simple XML project is no longer maintained. We recommend switching to the
+[JAXB converter](https://github.com/square/retrofit/tree/master/retrofit-converters/jaxb).
+
+-----
+
 A `Converter` which uses [Simple][1] for XML serialization.
 
 A default `Serializer` instance will be created or one can be configured and passed to the

retrofit-converters/simplexml/src/main/java/retrofit2/converter/simplexml/SimpleXmlConverterFactory.java

@@ -29,7 +29,10 @@ import retrofit2.Retrofit;
  * <p>
  * This converter only applies for class types. Parameterized types (e.g., {@code List<Foo>}) are
  * not handled.
+ *
+ * @deprecated we recommend switching to the JAXB converter.
  */
+@Deprecated
 public final class SimpleXmlConverterFactory extends Converter.Factory {
   /** Create an instance using a default {@link Persister} instance for conversion. */
   public static SimpleXmlConverterFactory create() {