Major update with exciting new features and improvements!

New: added gui.yml file to allow to tune the GUI items as wanted.
New: implemented /aach reset command to reset the statistics for an achievement category.
New: added support for BungeeTabListPlus, with achievement_count placeholder to display the player's number of achievements in the tab.
New: added SimplifiedReception config option to activate simpler effects and a calm sound when a player receives an achievement.
New: provided API so that third-party software can more easily pair with Advanced Achievements.

Improvement: removed chat header completely if no icon is set in the configuration.
Improvement: improved the overall stability and user experience of the plugin.
Improvement: enhanced performance.
Improvement: refactored large parts of the project to make it more maintainable and facilitate contributions.
Improvement: achievements are now driven by Bukkit Events so that third-party plugins can detect when they are awarded.

Fix: fixed broken permissions for sub-categories making use of metadata (Breaks, Places and Crafts achievements).
Fix: blocked double plant abuses with Fertilising achievements.

Other: removed MCStats Metrics, as project is abandoned.
Other: significantly improved the Wiki.
Other: removed AsyncPooledRequestsSender configuration option, plugin can no longer be set to run in single threaded mode.