Remove font weight from reset

This is causing havoc with bold and strong within phrasing elements
Simplify reverse functionality, make padding margin
Fix reverse again

Still can’t penetrate flex box. A more complicated approach must
remain. Gutters are wrong when columns reversed.
Remove max-width from .unbound images
Give unbound images auto height
Spine CSS as a table of contents

Building Spine CSS as a table of contents from partials, so the
different parts are not obscured by multiple build steps. Additional
reorganization can happen in future PRs, so it's easier to integrate
changes at deeper levels, and so we get the advantages of smaller files
earlier.