Typo fix: let's -> lets

Cosmetic change in css/main.css

clarification of vertical/horizontal slide relation

rm extrenous whitespace

Clarified a bit how horizontal and vertical slides relate.

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

now: eot, svg, ttf, woff

this way, more browsers are supported, like older Opera/Chrome/FF

improved accessibility 

added small fallback for non-font-face browsers

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

this way things are in Impact; Impact fits much more with the visual style than does the default Arial or Calibri.

use mq to reduce font size for low resultions, max limit on width for slides set to 900px (closes #49)

Made the slideshow responsive

Include speaker notes plugin after reveal.js 

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