Release 1.2.0

Added

• Show validation warnings for duplicate declarations
• Show validation warnings for missing references
• Option --validate to exit with status code 2 if document has
  warnings
• Option --quite to suppress output to console
• Optimize EBNF syntax as ( a ), { a } in diagram as a+ (one or more)
• Optimize EBNF syntax as a | { b } in diagram as choice with "skip",
  "a", or one or more "b"
• Optimize EBNF syntax as a | [ b ] in diagram as choice with "skip",
  "a", or "b"

Changed

• Long choice lists are now spread over multiple columns, if the
  length exceeds 10.
• Updated styling of document