/**
 * @class Subtree
 * @extends jibo.bt.Behavior
 * @memberof jibo.bt.behaviors
 * @description Encapsulates an external subtree file (`.bt` file) into a single behavior. This behavior fails if the
 * `.bt` tree fails, and succeeds if that tree succeeds.
 * @param {Object} options See {@link jibo.bt.Behavior|Behavior} for all options.
 * @param {String} options.behaviorPath The path to the `.bt` file this behavior encapsulates. This assumes the root
 *                          of all `.bt` files is in `${project}/behaviors`.
 * @param {Function} options.getNotepad Returns an object that will become this referenced tree's notepad. Think of this as the
 *                              arguments to this subtree.
 * @param {Function} options.onResult Called when the external tree either fails or succeeds. A result object is passed as an argument.
 *                            This result object is populated by the external tree. Think of this as the return value.
 */