Recursive binding

[thejohnfreeman]

Binders should be able to recurse by directly calling hd.bind. They should also be able to pass an object literal to extend the sub-context, e.g.:

{
  $index: i,
  $forloop: {
    $index: i,
    $next:  i+1,
    $prev:  i-1
  }
}

[thejohnfreeman]

Implemented in d2b037bd267c2c948a50162d06f1824e53f08729, but untested.