type definition improvements

[DamianoNaraku]

i'm not knowledgeable enough to submit a push request, so i'm publishing my proposed changes here.
use any git-based editor to check the differences.

// Project: https://github.com/joaonuno/tree-model-js
// Definitions by: Abhas Bhattacharya <https://github.com/bendtherules>
// TypeScript Version: 2.2

export = TreeModel;

declare class TreeModel<T extends Object = Object> {
    constructor(config?: TreeModel.Config<T>);

    private config: TreeModel.Config<T>;

    safe_parse<T>(model: TreeModel.Model<T>): TreeModel.Node<T>;
    parse<T>(model: TreeModel.Model<T>): TreeModel.Node<T>;
}

declare namespace TreeModel {
    class Node<T> {
        constructor(config: Config<T>, model: Model<T>);

        isRoot(): boolean;
        hasChildren(): boolean;
        addChild(child: Node<T>): Node<T>;
        addChildAtIndex(child: Node<T>, index: number): Node<T>;
        setIndex(index: number): Node<T>;
        getPath(): Array<Node<T>>;
        getIndex(): number;

        walk(options: Options, fn: NodeVisitorFunction<T>, ctx?: object): void; 
        walk(fn: NodeVisitorFunction<T>, ctx?: object): void;

        all(options: Options, fn: NodeVisitorFunction<T>, ctx?: object): Array<Node<T>>;
        all(fn: NodeVisitorFunction<T>, ctx?: object): Array<Node<T>>;

        first(options: Options, fn: NodeVisitorFunction<T>, ctx?: object): Node<T> | undefined;
        first(fn: NodeVisitorFunction<T>, ctx?: object): Node<T> | undefined;

        drop(): Node<T>;
        children: Node<T>[];
        config: Config<T>;
        model: Model<T>;
        [propName: string]: any; // is this really necessary? can it have dynamic properties that cannot be listed and typed individually?
    }

    interface Config<T> {
        /**
         * The name for the children array property. Default is "children".
         */
        childrenPropertyName?: keyof T;
        modelComparatorFn?: ComparatorFunction<T>;
        [propName: string]: any;
    }

    interface Options {
        strategy: StrategyName;
    }

    type StrategyName = "pre" | "post" | "breadth";

    type ComparatorFunction<T> = (node1: Node<T>, node2: Node<T>) => number; // this was typed as bool, but from js source it looks to be a number. results are confronted with <= 0
    type NodeVisitorFunction<T> = (visitingNode: Node<T>) => boolean;

    type Model<T> = T;
    // this was "T & { children?: Array<Model<T>> }"
    // it was partially wrong because the children key is not always "children", but a custom key in config.
    // since it re-typed it as "keyof T", it is already guaranteed to be a key of T without adding the  & { customkeyname?: Array<Model<T>> }
    // actually that whole type definition is redundant.
}