v2.5.15

• added ID-Caching, thanks to @chland & @joaocustodio (#222 & #227)
• added transaction-handling, thanks to @chland (#225)
• fixed control(), thanks to @manukieli (#236)
• updated non spanish language phrases, thanks to @manukieli
• enhanced add_subgroup() to check if group and subgroup already linked, thanks to @chland (#221)
• enhanced is_banned() return TRUE if user doesn't exists, thanks to @jmikerq (#233)