title: openxlsx add multiple lines on header/footer
body: <p>I am trying to build the headers of an excel xlsx  workbook  with some format.
  Some strings are too large and need wrapped it.</p>
  
  <p>But when I do it with <strong>strwrap</strong> adding <em>\n</em> character, setHeaderFooter tell me that I have more than three parameters </p>
  
  <p>for example:</p>
  
  <pre><code>require (openxlsx)
  require (tidyverse)
  
  wb0 &lt;- createWorkbook()
  addWorksheet(wb0, "Sheet 1")
  
  label &lt;- "&amp;B EJECUTIVOS DE CUENTA: &amp;B"
  value &lt;- "FANARA ARIEL GUSTAVO:476, BARETTO ANA SILVINA:34, NO APLICA:32, SANTOS MAXIMILIANO ARIEL:21, AVILA ROBERTO:19, REGGI PABLO:9, Otros:51"
  
  
  setHeaderFooter (
    wb0, sheet = 1
    , header = c ( 
      # "left side / izquierda"
      strwrap (
        x = paste0 (
            label, " "
          , substr (value, start = 1, stop = 360)
        )
        , width = 45
        , prefix = "\n", initial = ""
      )
      , "center header / centro"
      , "rigth side / derecha"
    ) 
    , footer = c (
      "&amp;[Date]"
      ,  NA
      , "&amp;[File]"
    )
  )    
  </code></pre>