title: Linq: join the results in a IEnumerable<string > to a single string
body: <p>how do i join the results in a IEnumerable to a single string?
  the IEnumerable contains 20 single letters, and  i want it to combine it to a single string.</p>
  
  <p>And out of curiousity: how would i join it with a separator, for example if the IEnumerable contains the strings a b c d e how can i join it to a,b,c,d,e?</p>
  
  <p>Michel</p>