resolves #192 add redirect producer for Apache httpd

• using mod_alias rather than mod_rewrite is advised when it is sufficient, as it is for us.
• Single httpd redirect facility, producing a single .htaccess file at the root of the site. This can be renamed and included in httpd.conf using an "include" in the appropriate section.

    Include /Users/david/projects/antora/simple-examples/multiple-components/page-aliases/build/site/_redirect.conf

Perhaps the instructions could go in the proposed page-aliases page, which currently has brief samples of the other outputs.