• Improve recovery for list entries without - prefix. When recovering, provide
  a more helpful error message suggesting the missing prefix.
• Fix a bug where block strings terminated by EOF were not given an implicit
  newline.
• Fix parsing of plain scalars starting with indicator characters (?, :, and -).
• Throw a FormatException when parsing self-referential collections instead of
  a StackOverflow. Yaml definitions with collections nested within themselves
  are unsupported.