Version 0.7
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*  proxy setup using in TGBot call or using set_proxy method (both takes
   a list of parameters passed to httr::use_proxy
* `group_id` utility function (it work the same as `bot_token` or
  `user_id`, by using the `R_TELEGRAM_GROUP_` prefix);
* `sendDice` method;
* `sendPoll` method;
* `sendChatAction` method;
* miscellaneous bugfixes.
