Improve inline_keyboard example app

[xeptore]

• [x] Add bot instance creation error handling to prevent meaningless errors, e.g., nil pointer dereference, which occurs when instantiation errors
• [x] Add answering callback query to callback handler with documentation

[negasus]

I think, if we use error check on bot init in this example, we should use this approach for all examples?

[xeptore]

@negasus, yup. That make sense. But it's a matter of being lazy 😃 and fixing only what came across my way. I can update only the bot instantiation logic for all examples similar to this one, if that's fine.

[negasus]

Thanks)