title: fread - multiple separators in a string
body: <p>I'm trying to read a table using fread.
  The txt file has text which look like:</p>
  
  <pre><code>"No","Comment","Type"
  "0","he said:"wonderful|"","A"
  "1","Pr/ "d/s". "a", n) ","B"
  </code></pre>
  
  <p>R codes I'm using is: <code>dataset0 &lt;- fread("data/test.txt", stringsAsFactors = F)</code> with the <a href="https://github.com/Rdatatable/data.table/wiki/Installation" rel="nofollow noreferrer">development version</a> of data.table R package.</p>
  
  <p>Expect to see a dataset with three columns; however:</p>
  
  <pre><code>Error in fread(input = "data/stackoverflow.txt", stringsAsFactors = FALSE) : 
  Line 3 starting &lt;&lt;"1","Pr/ "&gt;&gt; has more than the expected 3 fields.
  Separator 3 occurs at position 26 which is character 6 of the last field: &lt;&lt; n) ","B"&gt;&gt;. 
  Consider setting 'comment.char=' if there is a trailing comment to be ignored.
  </code></pre>
  
  <p>How to solve it?</p>