2.4.0

• added XML file format
• added combined lists; see #29
• aded a note about the fact that alpha-2 and alpha-3 codes are lowercase instead of uppercase as defined by ISO 3166-1; see #50
• fixed id of Sudan for Swedish language
• fixed broken SQL files
• changed folder structure in preparations for adding more data to the library; for now, countries moved to their own countries folder inside the data folder and the flags folder was moved inside the data folder