Added the API definition for `_mget`

rest-api-spec/api/mget.json

@@ -0,0 +1,49 @@
+{
+  "mget": {
+    "documentation": "http://elasticsearch.org/guide/reference/api/multi-get/",
+    "methods": ["GET", "POST"],
+    "url": {
+      "path": "/_mget",
+      "paths": ["/_mget", "/{index}/_mget", "/{index}/{type}/_mget"],
+      "parts": {
+        "index": {
+          "type" : "string",
+          "description" : "The name of the index"
+        },
+        "type": {
+          "type" : "string",
+          "description" : "The type of the document"
+        }
+      },
+      "params": {
+        "fields": {
+          "type": "list",
+          "description" : "A comma-separated list of fields to return in the response"
+        },
+        "parent": {
+          "type" : "string",
+          "description" : "The ID of the parent document"
+        },
+        "preference": {
+          "type" : "string",
+          "description" : "Specify the shards the operation should be performed on (default: random shard)"
+        },
+        "realtime": {
+          "type" : "boolean",
+          "description" : "Specify whether to perform the operation in realtime or search mode"
+        },
+        "refresh": {
+          "type" : "boolean",
+          "description" : "Refresh the shard containing the document before performing the operation"
+        },
+        "routing": {
+          "type" : "string",
+          "description" : "Specific routing value"
+        }
+      }
+    },
+    "body": {
+      "description" : "Document identifiers; can be either `docs` (containing full document information) or `ids` (when index and type is provided in the URL."
+    }
+  }
+}