Merge pull request #4 from yulijia/gh-pages

a new article 'Flipping Coins Simulation with R'
remove `auto: true` from _config.yml because `rake preview` already does this
smaller figure height and explicitly write interval=.3 in the code chunks
tweak the coin flipping article (including setting the random seed)
remove '-with-r' in the filename; it is boring
rebuild website
a new post "draw easter eggs"