There were still some nasty bugs in the last few versions, but many should be fixed by now!

The following changes have been done:
- Removed AdvancementManager#setSavePath because it caused too much trouble with the rest of the code
- Instead implememented new methods to get the JSON Save String yourself and save it wherever you want (File, MySQL Database, etc...):
AdvancementManager#getProgressJSON(Player player) Returns the progress JSON containing info about all the advancements in the current manager
AdvancementManager#getProgressJSON(Player player, String namespace ) Returns the progress JSON containing info about all advancements with namespace in the current advancement manager
AdvancementManager#loadProgress(Player player, String json, Advancement... advancementsLoaded) Will load all advancements in advancementsLoaded using the entered JSON String
- AdvancementManager#loadProgress(Player player, Advancement advancement) => AdvancementManager#loadProgress(Player player, Advancement... advancementsLoaded) Now supports multiple advancements to be loaded at once (less code has to be executed). Same applies to saveProgress!

Also, the following bugsfixes have been done:
- Saving Advancements no longer deletes old saved information but instead updates it
- Minor bug fixes