Add statistics API.

Fixes issue #330

src/main/java/org/kohsuke/github/Requester.java

@@ -622,6 +622,13 @@ class Requester {
                 return type.cast(Array.newInstance(type.getComponentType(),0));
             }
 
+            // Response code 202 means the statistics are still being cached.
+            // See https://developer.github.com/v3/repos/statistics/#a-word-about-caching
+            if (responseCode == 202) {
+                LOGGER.log(INFO, "The statistics are still being generated. Please try again in 5 seconds.");
+                return null;
+            }
+
             r = new InputStreamReader(wrapStream(uc.getInputStream()), "UTF-8");
             String data = IOUtils.toString(r);
             if (type!=null)