Implement and document new ldict-map.

doc/utils.md

@@ -96,6 +96,22 @@ is not already present in the dictionary ```ld```.
 
 Returns the list of keys stored in given dictionary.
 
+    (ldict-map proc ld)
+
+* ```proc``` - procedure accepting 1, 2 or 3 arguments
+* ```ld``` - a ldict instance
+
+Returns a new dictionary of the same type with all values processed by
+given procedure.
+
+If it accepts one argument, only the value is passed to it. If it
+accepts two values, the key and the value is passed to it. And lastly
+if it accepts three arguments, the key, value and numeric index
+(starting from 0) are passed to it.
+
+In all cases the value the procedure returns is taken as the new value
+for given key.
+
 ### IO
 
     (import util-io)