Remove trailing spaces.
index.html: Add some comments to clarify code.

Also fix indentation.
Be consistent with the quotes type.

* use single quotes inside double quotes
* remove unneeded quotes from posts' descriptions

This change is just cosmetic, since jekyll works fine either way but it's better not to complicate things.
css/icons.css: Improve readability of font face.
404.md: type/javascript is the default for script so remove it.