Improve the DX when a tweet is not published.

Hi!

I was having troubles sending tweets with this module after to debug the code the problem was my app but the module just returned true like if all went ok.

A good improvement would be make the methodTwitterPost::post return FALSE if something went wrong and log what went wrong.

Patch in my next comment.

we might want to update the SocialPostNetworkInterface::post documentation explaining to this method should return a bool maybe something like:

/**
   * Execute the posting action.
   *
   * Uses the underlying SDK library to publish to the social network.
   *
   * @return bool
   *    True if the post action was done properly, False otherwise
   */
  public function post();

Thanks.