title: Summing all columns by group
body: <p>I'm positive that this is an incredibly easy answer but I can't seem to get my head around aggregating or casting with Multiple conditions</p>
  
  <p>I have a table that looks like this:</p>
  
  <pre><code>&gt; head(df, n=10L)
     STATE  EVTYPE FATALITIES INJURIES
  1     AL TORNADO          0       15
  3     AL TORNADO          0        2
  4     AL TORNADO          0        2
  5     AL TORNADO          0        2
  6     AL TORNADO          0        6
  7     AL TORNADO          0        1
  9     AL TORNADO          1       14
  11    AL TORNADO          0        3
  12    AL TORNADO          0        3
  13    AL TORNADO          1       26
  </code></pre>
  
  <p>Obviously this goes on... What I want to do is to collapse by STATE and EVTYPE Summing Fatalities and Injuries as I go so if these 10 rows were my ful dataset the result would be a single row data frame of:</p>
  
  <pre><code>   STATE  EVTYPE FATALITIES INJURIES
  1     AL TORNADO          2       74
  </code></pre>
  
  <p>My Complete frame has many States and many EVTYPES</p>