message: add clone and layer functions
diff: @@ -58,6 +58,16 @@ namespace MakerJs.model {
  return childModel;
  }
  + /**
  + * Clone a model. Alias of makerjs.cloneObject(modelToClone)
  + *
  + * @param modelToClone The model to clone.
  + * @returns A clone of the model you passed.
  + */
  + export function clone(modelToClone: IModel): IModel {
  + return cloneObject(modelToClone);
  + }
  +
  /**
  * Count the number of child models within a given model.
  *
  @@ -110,6 +120,21 @@ namespace MakerJs.model {
  return getSimilarId(modelContext.paths, pathId);
  }
  + /**
  + * Set the layer of a model. This is equivalent to:
  + * ```
  + * modelContext.layer = layer;
  + * ```
  + *
  + * @param modelContext The model to set the layer.
  + * @param layer The layer name.
  + * @returns The original model (for cascading).
  + */
  + export function layer(modelContext: IModel, layer: string): IModel {
  + modelContext.layer = layer;
  + return modelContext;
  + }
  +
  /**
  * Moves all of a model's children (models and paths, recursively) in reference to a single common origin. Useful when points between children need to connect to each other.
  *
  