Added xml headers to the get response and request

docs/samples/request_get.xml

@@ -1,7 +1,8 b''
+<?xml version="1.1" encoding="UTF-8" ?>
 <request version="1" type="get">
     <model>post</model>
     <filter>
         <id>id1/1</id>
         <id>id2/56</id>
     </filter>
 </request>

docs/samples/response_get.xml

@@ -1,31 +1,32 b''
+<?xml version="1.1" encoding="UTF-8" ?>
 <response>
     <status>success</status>
     <models>
         <post>
             <id>id1/1</id>
             <title>13</title>
             <text>Thirteen</text>
             <thread>id1/12</thread>
             <pub-time>12</pub-time>
             <edit-time>13</edit-time>
             <previous-id>id1/3,id23/5</previous-id>
             <after-id>id2/3,id43/5</after-id>
         </post>
         <post>
             <id>id1/2</id>
             <title>13</title>
             <text>Thirteen</text>
             <pub-time>12</pub-time>
             <edit-time>13</edit-time>
             <tags>
                 <tag>tag1</tag>
             </tags>
         </post>
         <post>
             <id>id2/1</id>
         </post>
         <post>
             <id>id2/5</id>
         </post>
     </models>
 </response>