Disable submenu generation.
Expand the sed template for more functionality.

Provide the page_title (normalized value of the page source filename).
Support templated header/footer "active" class - ${active_./page.md}
will evaluate to "active" when that page is templated.
Cleanup unused variables. May or may not be wanted, but required for the
${active_$1} variable.
Expand on the ${active_$1} macro - inactive links return inactive, not
blank.