[Doc] copy_to using attachment field type

If you want to use [copy_to](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/mapping-core-types.html#copy-to)
feature, you need to define it on each sub-field you want to copy to another field:

```javascript
PUT /test/person/_mapping
{
  "person": {
    "properties": {
      "file": {
        "type": "attachment",
        "path": "full",
        "fields": {
          "file": {
            "type": "string",
            "copy_to": "copy"
          }
        }
      },
      "copy": {
        "type": "string"
      }
    }
  }
}
```

In this example, the extracted content will be copy as well to `copy` field.

Closes #97.
(cherry picked from commit f4f6b57)
(cherry picked from commit 5878a62)

README.md

@@ -117,6 +117,37 @@ In the above example, the actual content indexed is mapped under `fields` name `
 it will only be available in the `_all` field. The other fields map to their respective metadata names, but there is no 
 need to specify the `type` (like `string` or `date`) since it is already known.
 
+Copy To feature
+---------------
+
+If you want to use [copy_to](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/mapping-core-types.html#copy-to)
+feature, you need to define it on each sub-field you want to copy to another field:
+
+```javascript
+PUT /test/person/_mapping
+{
+  "person": {
+    "properties": {
+      "file": {
+        "type": "attachment",
+        "path": "full",
+        "fields": {
+          "file": {
+            "type": "string",
+            "copy_to": "copy"
+          }
+        }
+      },
+      "copy": {
+        "type": "string"
+      }
+    }
+  }
+}
+```
+
+In this example, the extracted content will be copy as well to `copy` field.
+
 Querying or accessing metadata
 ------------------------------
 

src/test/java/org/elasticsearch/plugin/mapper/attachments/test/SimpleAttachmentIntegrationTests.java

@@ -27,6 +27,7 @@ import org.elasticsearch.index.mapper.MapperParsingException;
 import org.elasticsearch.plugins.PluginsService;
 import org.elasticsearch.test.ElasticsearchIntegrationTest;
 import org.junit.Before;
+import org.junit.Ignore;
 import org.junit.Test;
 
 import static org.elasticsearch.client.Requests.putMappingRequest;
@@ -149,4 +150,42 @@ public class SimpleAttachmentIntegrationTests extends ElasticsearchIntegrationTe
         assertThat(name, is(dummyName));
     }
 
+    /**
+     * As for now, we don't support a global `copy_to` property for `attachment` type.
+     * So this test is failing.
+     */
+    @Test @Ignore
+    public void testCopyTo() throws Exception {
+        String mapping = copyToStringFromClasspath("/org/elasticsearch/index/mapper/copy-to/copy-to.json");
+        byte[] txt = copyToBytesFromClasspath("/org/elasticsearch/index/mapper/xcontent/text-in-english.txt");
+
+        client().admin().indices().putMapping(putMappingRequest("test").type("person").source(mapping)).actionGet();
+
+        index("test", "person", jsonBuilder().startObject().field("file", txt).endObject());
+        refresh();
+
+        CountResponse countResponse = client().prepareCount("test").setQuery(queryStringQuery("Queen").defaultField("file")).execute().get();
+        assertThat(countResponse.getCount(), equalTo(1l));
+
+        countResponse = client().prepareCount("test").setQuery(queryStringQuery("Queen").defaultField("copy")).execute().get();
+        assertThat(countResponse.getCount(), equalTo(1l));
+    }
+
+    @Test
+    public void testCopyToSubField() throws Exception {
+        String mapping = copyToStringFromClasspath("/org/elasticsearch/index/mapper/copy-to/copy-to-subfield.json");
+        byte[] txt = copyToBytesFromClasspath("/org/elasticsearch/index/mapper/xcontent/text-in-english.txt");
+
+        client().admin().indices().putMapping(putMappingRequest("test").type("person").source(mapping)).actionGet();
+
+        index("test", "person", jsonBuilder().startObject().field("file", txt).endObject());
+        refresh();
+
+        CountResponse countResponse = client().prepareCount("test").setQuery(queryStringQuery("Queen").defaultField("file")).execute().get();
+        assertThat(countResponse.getCount(), equalTo(1l));
+
+        countResponse = client().prepareCount("test").setQuery(queryStringQuery("Queen").defaultField("copy")).execute().get();
+        assertThat(countResponse.getCount(), equalTo(1l));
+    }
+
 }

src/test/resources/org/elasticsearch/index/mapper/copy-to/copy-to-subfield.json

@@ -0,0 +1,19 @@
+{
+  "person": {
+    "properties": {
+      "file": {
+        "type": "attachment",
+        "path": "full",
+        "fields": {
+          "file": {
+            "type": "string",
+            "copy_to": "copy"
+          }
+        }
+      },
+      "copy": {
+        "type": "string"
+      }
+    }
+  }
+}

src/test/resources/org/elasticsearch/index/mapper/copy-to/copy-to.json

@@ -0,0 +1,13 @@
+{
+    "person": {
+        "properties": {
+            "file": {
+                "type": "attachment",
+                "copy_to": "copy"
+            },
+            "copy": {
+              "type": "attachment"
+            }
+        }
+    }
+}