Added input button support

[csanz]

I added input button support, super simple fix.

  var rel = $(this).attr('rel') 
  var href = $(this).attr('href') 

and updated the readme file:

jQuery(document).ready(function($) {
  $('a[rel*=facebox]').facebox()
  $('input[rel*=facebox]').facebox()
})

   <input type="button" value="Sign Up" href="sign-up.html" rel="facebox[.body]">
  Loads the sign-up.html page