Introduced to org-latex-feature-implementations in this commit:
+ :when keyword
+ :prevents keyword
+ special treatment of features starting with !
No more universal preamble.
Moved all latex template content other than font into preamble features.
Added xkcd feature implications.
Refactored org-latex-generate-features-preamble.
Update org-latex-clever-preamble graphic to better illustrate the
functionality.
TEC
