Add the useful intersection of sanitize.py

From stagestosaturn.git and chariotsforapollo.git
Add a skeleton EPUB structure and Makefile

Use style="width: 100%" instead of width="100%" on the cover image,
since that makes cover.html validate and still works.
Merge common infrastructure from epubbase

Conflicts:
	.gitignore
	Makefile
	OEBPS/.gitignore
	OEBPS/content.opf
	OEBPS/toc.ncx
	sanitize.py
	stylesheet.css
Reduce differences from epubbase

The generated EPUB has been verified to have no unexpected changes
compared to commit e33e55e367044126b361dda0b2ab50ccece796f9.