Added annotation aliases (class and internal).

I added two aliases for existing annotation names because, depending on someone's programming background, these aliases might make a bit more sense.

The new annotation name `package` is confusing because a package is typically a container for classes, not a visibility keyword, so I have added the annotation name `internal` as an alias for `package`.

````
/** @package */
/** @internal */
````

The annotation name `constructor` is fine but while I working on this update I thought it might be nice to have the annotation name `class` available as an alias for `constructor`. In ES6+ the keyword `class` will be used, not `constructor`, so I believe this alias blends nicely into the mix.

````
/** @constructor */
/** @class */
````

I have tested these aliases on some code of mine and they appear to work as intended.