Split out the current Collection class into two new Collection and OpenCollection classes as part of  https://github.com/craterdog/java-collection-framework/issues/9.
Refactored the Iteratable and Accessible interfaces, and added a ClosedCollection abstract class as part of  https://github.com/craterdog/java-collection-framework/issues/9.
Removed all inheritance between interfaces as part of  https://github.com/craterdog/java-collection-framework/issues/9.
Decoupled interfaces from abstractions as part of  https://github.com/craterdog/java-collection-framework/issues/9.