Add editor temporary saves and .DS_Store to .gitignore.
TemplateLoader should have overridden load().

There is no "load_template".
Add did_site_change predicate before committing.

We don't want to quite unnecessary changes, so test it before
committing.
Update build-site usage documantion.
Return stdout and stderr to git callers.
Clean up the working tree after checking it out.

This way, we don't have obsolete files hanging around if they
get removed from the source repo.
Module for manipulating images.

Right now, we just resize.
Add gen_images_dirs() for generating chapters of images.

This will recursively process directories, looking for png files and
creating the html files for them.