Triggerable command chains

[DeltaWhy]

There should be a way to define a non-repeating command chain that can be triggered when needed. Useful for rare events like game start. Syntax idea:

chain :game_start 1, 2, 3, 5, 5, 5 do
  # ...
end
at some_location_with_a_button do
  activate :game_start
  # trigger is already a Minecraft command so we can't call it that
end