Add "$foreach" statement.

[ciukstar]

Add a new construct "$foreach" that works like $forall but yields the current element along with the remaining elements.

Usage:

[hamlet|
   <ul>
      $foreach (curr, rest) <- elements
          <li>#{show curr}
          $if not (null rest)
              <hr> 
|]

Compared with:

[hamlet|
    <ul>
         $with n <- length  elements
             $forall (i,curr) <- zip irange elements
                 <li>#{show curr}
                 $if i /= n
                     <hr>
|]

where 
    irange = [ 1 :: Int .. ]