Adds passed node as child or creates new child
@param {AbbreviationNode} child
@param {Number} position Index in children array where child should
be inserted
@return {AbbreviationNode}
function(child, position) {
			child = child || new AbbreviationNode;
			child.parent = this;
			
			if (_.isUndefined(position)) {
				this.children.push(child);
			} else {
				this.children.splice(position, 0, child);
			}
			
			return child;
		}