message: add Mat3.isIdentity
diff: * furnished to do so, subject to the following conditions:
  */
  -import { Mat4, Vec3 } from '../3d'
  +import { Mat4, Vec3, EPSILON } from '../3d'
  import { NumberArray } from '../../../mol-util/type-helpers';
  interface Mat3 extends Array<number> { [d: number]: number, '@type': 'mat3', length: 9 }
  @@ -118,6 +118,11 @@ namespace Mat3 {
  return out;
  }
  + const _id = identity();
  + export function isIdentity(m: Mat3, eps?: number) {
  + return areEqual(m, _id, typeof eps === 'undefined' ? EPSILON : eps);
  + }
  +
  export function hasNaN(m: Mat3) {
  for (let i = 0; i < 9; i++) if (isNaN(m[i])) return true
  return false
  