Add blank interfaces for future refactoring
Add action input/output format description
add minitest-reporters
Add World#subscribed_actions

along with World#subscription_index and Action.all_children
remove old executor
add some argument checking on initialization
add test for World#subscribed_actions method
Add PersistenceAdapters::SimpleFileStorage

with tests
also fix PersistenceAdapters::Memory
whitespace
whitespace
Fix 'string' vs :symbol issue when storing with SimpleFileStorage

add tests for it
Add PersistenceAdapters::ActiveRecord with tests
Deserialize running step action
Parenthesis
World#subscribed_actions takes class instead of action

Problem with action.class returning unexpected class when passing
"phased" action instance.
Flow generating algorithm

It generates run flow based on the dependencies between run steps.
Extract Action#class.superclass to Action.action_class
Use id instead of object reference for plan_step in action

Also, we don't need to store run_step in action, just output_reference
Whitespace - one-line hash
Use attribute instead of instance variable when possible