Fix h1 end tag in Sphinx header titles

A </h1> end tag was incorrectly written as <h1>.  Also adjust style
settings so that the resulting computed style remains the same for
div.rel.
Fix typos in layout.html

There were multiple misplaced semicolons, etc.
Fix "search" accesskey in layout.html

The accesskey for the "search" link conflicted with the one for the
"contents" link.
Consolidate style settings in kerb.css

Move style settings that were previously in layout.html to kerb.css.
Rename kerb.css kerb.css_t, making it a template, to allow
parameterized style settings to remain parameterized.
Reduce copied code in layout.html

layout.html unneccesarily copied code from the parent
agogo/layout.html content block just to alter the sidebar.  Override
various subblocks of the sidebar instead.
Refactor rellinks formatting in layout.html