title: Plot normal, left and right skewed distribution in R
body: <p>I want to create 3 plots for illustration purposes:
   - normal distribution
   - right skewed distribution
   - left skewed distribution</p>
  
  <p>This should be an easy task, but I found only <a href="http://www.statmethods.net/advgraphs/probability.html" rel="noreferrer">this link</a>, which only shows a normal distribution. How do I do the rest?</p>