refactor: improve diagram layout and edge clipping

- Use native shape for all states (with and without actions) so
  Graphviz clips edges at the actual rounded border
- States with actions embed a border=0 HTML TABLE inside the native
  shape for UML compartment layout
- Transition labels use HTML tables for better spacing
- Escape guard conditions with HTML entities
- Increase ranksep to 0.3, enable forcelabels, add labeldistance
- Regenerate all documentation images

Author: fgmacedo