gh-pages: update to specl 6.

Rather than repasting the specl.md file into the web based site
generator for every release, break out the existing theme so that
I can rebuild the docs site with jekyll command line.
* _config.yml: New file. Configuration.
* _layouts/default.html: New file. Old theme with the content
ripped out.
* index.html: Remove.
* index.md: Copied from master v6 tag.
* javascripts/main.js: Add terminating newline.
* stylesheets/styles.css: Don't put inline <code/> on a black
background, and reduce the padding somewhat.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>