Update SOTD, figures, and section refs (#5)

* Update SOTD on section refs
* Remove PNG version of figures and update SVG to correct erratum and to use RDF 1.2, rather than RDF 1.1.
* Update figure2 for accessibility.
  Image components use **bold text**.

Co-authored-by: Andy Seaborne <[email protected]>
Co-authored-by: Pierre-Antoine Champin <[email protected]>
Co-authored-by: Ted Thibodeau Jr <[email protected]>

Author: 4 people