code: function dims( arr, d, depth ) {
  	if ( depth && isArray( arr ) ) {
  		d.push( arr.length );
  		dims( arr[ 0 ], d, depth-1 );
  	}
  	return d;
  }
docs: FUNCTIONS // 
  FUNCTION: dims( arr, d, depth )
  Determines matrix dimensions.
  
  @param {Array} arr - input array
  @param {Number[]} d - dimensions array
  @param {Number} depth - maximum number of dimensions
  @returns {Number[]} array of dimensions