Use a single index.htm for development and building

Use HTML comments to enable development lines and disable build lines,
then use a filter script remove development lines and enable build lines
when generating the static files.

The HTML comments are a bit ugly, but I prefer that to the confusion
of having two different files and then having to maintain them both.
Make the env filter more consistent/intuitive
Space out the template and remove blank lines during build

Makes the whole thing easier to read/manage.