+ allowRedirect count option to get the redirect key's value
+ Subkey Error Classes and import the levelup errors
* [bug] codec/legacy.js missing buffer=false
+ set InterfacedObject maxListeners to Infinity.
+ nut.isAlias
* [bug] nut.createSubkey addRef judge error.
* move properties getter/setter to Subkey.prototype
+ Subkey.loadValue
+ load key value to Subkey.value automatically when Subkey be created.
  + load the real key to Subkey._realKey if key value is an alias
+ add aReadyCallback argument to Subkey.init(readyCallback) method
+ add aReadyCallback argument to Subkey.subkey(name, options, readyCallback)
  * readyCallback(err, theKey)
+ Subkey.put itself to database
  * Subkey.put(callback): = put(@path(), @value)
  * Subkey.put(value, callback) = put(@path(), value)
* using dispatchError(LevelUp) on Subkey.get