Store realtime object to instance variable.

[mazgi]

This feature enable both following:

https://github.com/aki017/slack-ruby-gem/blob/dev/examples/rtm.rb#L7-L11

rtm = client.realtime
rtm.on :message do |m|
  p m
end
rtm.start

and

client.realtime.on :message do |m|
  p m
end
client.realtime.start

[ioquatix]

How does this work if you want multiple connections?