This task   (the reverse of   URL encoding   and distinct from   URL parser)   is to provide a function
or mechanism to convert an URL-encoded string into its original unencoded form.



Test cases

   The encoded string   "http%3A%2F%2Ffoo%20bar%2F"   should be reverted to the unencoded form   "http://foo bar/".
   The encoded string   "google.com/search?q=%60Abdu%27l-Bah%C3%A1"   should revert to the unencoded form   "google.com/search?q=`Abdu'l-Bahá".


"http%3A%2F%2Ffoo%20bar%2F".pump(String,  // push each char through these fcns:
   fcn(c){ if(c=="%") return(Void.Read,2); return(Void.Skip,c) },// %-->read 2 chars else pass through
   fcn(_,b,c){ (b+c).toInt(16).toChar() })  // "%" (ignored)  "3"+"1"-->0x31-->"1"