This break doesn't match https://github.com/Bukkit/Bukkit/blob/master/CONTRIBUTING.md
Javadocs are limited to 78 chars, but code isn't limited at all.

I also think that everywhere you have this
```java
    /*
     * @param achievement
     *            the {@link Achievement} that should be displayed
     */
```
You should have this
```java
    /*
     * @param achievement the {@link Achievement} that should be displayed
     */
```
Unless it's longer than 78 chars, in this case it would be like
```java
    /*
     * @param achievement the {@link Achievement} that should be displayed
     *     and this is the reste of achievement description (4 spaces)
     */
```
For that last thing I never really understood the format of this kind of in-JD indentation, but maybe if I randomly ping @Wolvereness he could explain? My last PR to https://github.com/Bukkit/Bukkit-JavaDoc was entirely reformated x)