Add support for specifying event `if` conditions with a method name symbol

[virtualstaticvoid]

Add the ability to define if conditions for events using an instance method name symbol, in addition to the already supported proc or lambda way.

state :off
  event :turn_on, :transition_to => :on,
                  :if => :sufficient_battery_level?

  event :turn_on, :transition_to => :low_battery,
                  :if => proc { |device| device.battery_level > 0 }
end

# corresponding instance method
def sufficient_battery_level?
  battery_level > 10
end

Here, the :sufficient_battery_level? method is invoked when evaluating the condition.

[virtualstaticvoid]

Hi @geekq

Sorry to bug you. Have you had a chance to review this pull request, and if so could it be merged? It would really be great if conditions could be specified using this technique which is a familiar pattern in Rails.

Thanks

[virtualstaticvoid]

Awesome, thanks for merging!

[hmaack]

:+1: