v4.0.0

• ⚠️ While there are no breaking API changes, the data has been revamped considerably. It's a good idea to test your integration before adopting this version, especially if you are accessing the GeoJSON directly.
• Add 100 new features for higher granularity
• Add vehicle height restriction unit data and endpoint: roadHeightUnit (#30, thanks @1ec5 )
• Add endpoints to fetch all identifiers for a location:
  • iso1A2Codes
  • iso1A3Codes
  • iso1N3Codes
  • m49Codes
  • wikidataQIDs
  • emojiFlags
• Add endpoint to check United Nations membership status: isInUnitedNations
• Add maxLevel coding option
• Add new level values: subcountryGroup, sharedLandform, subunion, unitedNations
• Derive attribute data of group features from their member features when possible
• Ensure every features has geometry or member features, but not both
  • For example, China's geometry is now represented by new separate feature, Mainland China, along with the existing Hong Kong and Macau features
• Ensure every stack of features has only one feature per level (except North America, which is defined this way in M49)