Added xml headers to the get response and request

docs/samples/request_get.xml

@@ -1,3 +1,4 b''
+<?xml version="1.1" encoding="UTF-8" ?>
 <request version="1" type="get">
     <model>post</model>
     <filter>

docs/samples/response_get.xml

@@ -1,3 +1,4 b''
+<?xml version="1.1" encoding="UTF-8" ?>
 <response>
     <status>success</status>
     <models>