title: Shapeless: flatMap over tuple fails to compile
body: <p>Using shapeless and an example from the tutorial:</p>
  
  <pre><code>import shapeless._
  import syntax.std.tuple._
  import poly._
  
  object ShapelessPlay extends App{
  
    val t = ((1,"a"),'c')
  
    println(t flatMap identity)
  }
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>could not find implicit value for parameter mapper: shapeless.ops.tuple.FlatMapper[((Int, String), Char),shapeless.poly.identity.type]
  </code></pre>
  
  <p>println(t flatMap identity)</p>
  
  <p>What am I missing?
              ^</p>