Add preface and fix title of blanchard10a. Fixes #5.
Add preface to v10. Fixes #6.
Add preface to v13 and remove institution in author fields. Fixes #7.
Add preface to v15. Fixes #9.
Add discussion for tillman11a. Still needs tweaking.
Add preface to v17. Fixes #15.
Add preface to v19. Fixes #17.
Add preface to v20. Fixes #18.