Fixed #644
Update jquery.fancybox.css.

* put separate elements in a new line
* remove unit from 0
* fix typo in comment
README.md improvements:

* use Markdown syntax where possible
* break long lines
* fix typos
css: use tabs for consistency.
Update jquery.mousewheel to v3.1.3.
CHANGELOG.md: use two blank lines before each version for consistency.
Optimize images.

Use kraken.io, `PNGOut /r` and https://github.com/subzey/zopfli-png.
Fix various JSHint warnings and keep the style consistent.