Moved format-specific code to separate files

The format-specific engine code for Jonah and Sugarcane has been moved
out of the "header.html" files into "code.js" files within each targets
subdirectory. Also, Responsive now transcludes Sugarcane's code into
itself, saving the need to maintain two copies.

Also, decided to reconsider and remove lastlink(), for at least the
moment.