Remove stray space after `alt=`.
index.html: remove unneeded class.

It's inherited from `ul`.
Use a 16x16 favicon.ico.
Use the https links to the github projects for consistency.
Fix links.

* use the https links to GitHub for consistency
* fix kramdown links target
Update .gitignore and _config.yml.

* ignore "package.json" in "_config.yml" too
* remove unneeded ignores from "_config.yml"