Xcode 13 support and `standard` row delimiter

• Xcode 13 has been supported by raising the iOS requirements to iOS 11.
  The library still supports iOS 7+, but the SPM now defines iOS 11+. If you want to support older OSes, modify the SPM manifest.
• Support for more than one row delimiter (e.g. for the standard \r\n and \n) at the same time.
  CSVReader will end a row when one of the row delimiters is encountered. Use just one row delimiter for better performance.