constructor(key) {
    // Call the super constructor.
    super();
    // If a key key was provided.
    if (key) {
      // If this is a string...
      if (typeof key === 'string') {
        this.parseKey(key);
      }
      else if (
          this.hasPrivateKeyProperty(key) ||
          this.hasPublicKeyProperty(key)
      ) {
        // Set the values for the key.
        this.parsePropertiesFrom(key);
      }
    }
  }
Create a new JSEncryptRSAKey that extends Tom Wu's RSA key object.
This object is just a decorator for parsing the key parameter
@param {string|Object} key - The key in string format, or an object containing
the parameters needed to build a RSAKey object.
@constructor