Add OCB glossary entry as well as AEAD mode glossary entry
Fix GCM entry to be consistent with other entry
Improve AEAD description
Use AEAD definition for GCM mode
Basic OCB section
Improve markup for OCB citation
AEAD modes of operation -> AEAD modes
Add fancy illustration command
Improve illustration command
Add AEAD illustration
Decrease size of AEAD illustration
Work on OCB mode, including illustrations
Improve line spacing