Do not stop processing even if gh query fails

It gives warnings now instead.
Support GitHub pages entries
Support repository and homepage fields
Add test for a git repo that doesn't end in .git
Make walker accept more repository variants

Looks like people have many ways to declare that.
Support github.io for GitHub Pages
Write output files in series

Previously it was missing some files. Likely a couple can be written in
parallel. Nicer to deal with it this way, though.