ashblue / fluid-behavior-tree

Add icons for representing RepeatForever, RepeatUntilFailure, and RepeatUntilSuccess in the
visualizer

Adds documentation for RepeatForever, RepeatUntilSuccess, and RepeatUntilFailure to README.md

Now that DecoratorBase returns failure if it has no child, Does_not_crash_if_no_child can be moved
to the base decorator tests

Remove unneeded local variables, and let the three new decorators return `TaskStatus.Failure` if
they have no child

 into jtg/repeater

RepeatForever, RepeatUntilSuccess, and RepeatUntilFailure are new decorators used to continue a task
indefinitely.  RepeatForever executes its child and returns TaskStatus.Continue, regardless of its
child's return status.  RepeatUntilSuccess returns TaskStatus.Success if its child returns success,
else it returns TaskStatus.Continue.  RepeatUntilFailure returns TaskStatus.Failure if its child
returns failure, else it returns TaskStatus.Continue.