Fix small misspelling: Mardown -> Markdown
Merge pull request #883 from seanfisk/fix-small-misspelling

fix small misspelling: Mardown -> Markdown
add contribution guidelines from dev
Merge branch 'master' of github.com:hakimel/reveal.js
use node.js 0.10
Merge pull request #1 from hakimel/master

Update from origin