Implemented the offset parameter for the getUpdates API call according to https://core.telegram.org/bots/api#getupdates
In short: the offset is calculated by adding 1 to the id of the last received Update.
Caching messages in a list is now redundant, so the cache is removed. Only the id of the last received Update is kept for future getUpdates calls.
- TeleBot#get_update now makes use of this argument, which improves the efficiency of the method.
- Removed useless req.status_code statement in apihelper.py#send_data
pieter