Add new metrics and handle errors gracefully

- Handle plugins errors gracefully
- Add issue comments and organization metrics

README.md

@@ -138,11 +138,10 @@ Assuming your username is `my-github-user`, you can embed your metrics in your p
 <summary>💬 Restrictions and fair use</summary>
 
 Since GitHub API has rate limitations and to avoid abuse, the shared instance has the following limitations :
-  * Images are cached for 2 hours
+  * Images are cached for 1 hour
     * Your generated metrics **won't** be updated during this amount of time
-    * If you enable or disable plugins by changing the url parameters, you'll need to wait before changes are applied
-  * You're limited to 3 requests per 2 hours
-    * Restriction **does not** apply to already cached users metrics, including your own
+    * If you enable or disable plugins in url parameters, you'll need to wait for cache expiration before these changes are applied
+  * A rate limiter prevents new metrics generation when reached, but it **does not** affect already cached users metrics, including your own
   * Most of plugins are not available
     * PageSpeed plugin can be enabled by passing `?pagespeed=1`, but metrics generation can take up some time