title: io.WriteSeeker and io.ReadSeeker from []byte or file
body: <p>I have a method called "DoSomething".  DoSomething will take binary source data perform an operation on it, and write out binary data.  DoSomething needs to be generic enough to handle either a []byte array or a file handle for both the source and destination.  To accomplish this, I have attempted to declare the method like this:</p>
  
  <p><code>func DoSomething(source *io.ReadSeeker, destination *io.WriteSeeker)</code></p>
  
  <p>I have implemented the ReadSeeker and WriteSeeker for working with buffers, using my own custom, required methods (if there is a way to automatically accomplish this, I'd love to hear about it as well). 
  Unfortunately, I can't seem to figure out how to create either an io.ReadSeeker or io.WriteSeeker from a file handle.  I'm fairly sure there must be some pre-cooked way of handling this without having to manually implement them.  Is this possible?</p>