New methods from bot api v3.5

Collect all api helper-methods in Client::ApiHelper module.
Add bin/fetch-telegram-methods to update methods list from website.

README.md

@@ -532,6 +532,8 @@ To release a new version, update the version number in `version.rb`,
 and then run `bundle exec rake release`, which will create a git tag for the version,
 push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).
 
+Use `bin/fetch-telegram-methods` to update API methods list from Telegram website.
+
 ## Contributing
 
 Bug reports and pull requests are welcome on GitHub at https://github.com/telegram-bot-rb/telegram-bot.