Fix validation errors.

All validation errors are fixed except for the `http-equiv="X-UA-Compatible"` meta tag which is known to not be HTML5 valid but is needed in order to force usage of the latest IE.
Update readme.md.

* fix typos
* use a code block for the local commands
Update .gitignore and _config.yml.

Ignore "package.json" in _config.yml too.
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