function apply_transform( array, start, length, matrix )
	{
		var l = start + length;
		for(var i = start; i < l; i+=3)
		{
			var v = array.subarray(i,i+3);
			vec3.transformMat4( v, v, matrix );
		}
	}
Returns a mesh with all the meshes merged (you can apply transforms individually to every buffer)
@method Mesh.mergeMeshes
@param {Array} meshes array containing object like { mesh:, matrix:, texture_matrix: }
@param {Object} options { only_data: to get the mesh data without uploading it }
@return {GL.Mesh|Object} the mesh in GL.Mesh format or Object format (if options.only_data is true)