checkpoint
Writing a BetterToC again.  Same as ToC, only it also shows orphaned pages.
Now writing pages
Used for book generation
Generate .epub file
(we're still missing metadat at this point)
Builds - but untested.

Need to start validating.
Need to also rewrite image urls; and cache remote images
from github.
stage
Caching of images.  Copying of images to output dir.  Next: metadata for images
images now part of metadata