Add tasks for all the new languages

Task/Levenshtein-distance/Nim/levenshtein-distance.nim

@@ -0,0 +1,24 @@
+import sequtils
+
+proc levenshteinDistance(s1, s2): int =
+  var (s1, s2) = (s1, s2)
+
+  if s1.len > s2.len:
+    swap s1, s2
+
+  var distances = toSeq(0..s1.len)
+
+  for i2, c2 in s2:
+    var newDistances = @[i2+1]
+    for i1, c1 in s1:
+      if c1 == c2:
+        newDistances.add(distances[i1])
+      else:
+        newDistances.add(1 + min(distances[i1], distances[i1+1],
+                                 newDistances[newDistances.high]))
+
+    distances = newDistances
+  result = distances[distances.high]
+
+echo levenshteinDistance("kitten","sitting")
+echo levenshteinDistance("rosettacode","raisethysword")