Changes for v0.1.1

  - Ignore_missing is now a read-only attribute.
  - Added _path key that tracks the path in the data structure.
  - The _index key is now deprecated.
  - Added more modules to the SEE ALSO section.
  - Corrected POD: ignore_missing is true by default.
  - Minor code tweaks.
  - Explicit prerequsite for Test::Differences that caused failures
    for some CPAN Testers.