SuperbChemistry 3.0

SuperbChemistry 3.0

- Update for compatibility with modern versions of OpenOffice and
  LibreOffice.  One of the regular expressions contained an unescaped [
  in a character class, which no longer works because it now denotes a
  named character class.  Also, work around a bug in LibreOffice undo.

- Put all actions taken during a formatting pass in an undo context so
  they can be undone and redone as a unit.

- Change the file extension to oxt and add full extension metadata and a
  menu item.

- Add support for formatting a selection rather than the entire
  document, with a minor limitation.

- Make the rules for recognizing sequences slightly more conservative.