title: Convert from lowercase to uppercase all values in all character variables in dataframe
body: <p>I have a <a href="https://dl.dropboxusercontent.com/u/1791181/multcol.csv" rel="noreferrer">mixed dataframe</a> of character and numeric variables. </p>
  
  <pre><code>city,hs_cd,sl_no,col_01,col_02,col_03
  Austin,1,2,,46,Female
  Austin,1,3,,32,Male
  Austin,1,4,,27,Male
  Austin,1,5,,20,Female
  Austin,2,2,,42,Female
  Austin,2,1,,52,Male
  Austin,2,3,,25,Male
  Austin,2,4,,22,Female
  Austin,3,3,,30,Female
  Austin,3,1,,65,Female
  </code></pre>
  
  <p>I want to convert all the lower-case characters in the dataframe to uppercase. Is there any way to do this in one shot without doing it repeatedly over each character-variable?</p>