Typo fix: let's -> lets

themes are now available as separate css files under css/theme/, old theme option in config is no longer supported (closes #104)

I gave all the <img>s alt attributes, which makes reveal.js a lot more accessible

Must be called after reveal.js otherwise the Reveal object is undefined
and the plugin can't add it's event listener.

add beige theme, move theme class from .reveal to document element, use log instead of alert to demonstrate custom events