* types chapter & candidate types
* Factor out some message types
* backing and availability types.
* spacing
* finish thought
* info on signed payloads
* update links
* explicit wrapper types
* add remaining message types
* add runtime API subsystem
* adjust language
* tweak candidate validation message
* find homes for some misfit types
* embed abridged within full candidate receipt
* Update roadmap/implementors-guide/src/SUMMARY.md
Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>
* Update roadmap/implementors-guide/src/SUMMARY.md
Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>
* adjust text on candidate selection message to match
Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>