Add tasks for all the new languages

Task/Generator-Exponential/Nim/generator-exponential.nim

@@ -0,0 +1,40 @@
+proc `^`*(base: int, exp: int): int =
+  var (base, exp) = (base, exp)
+  result = 1
+
+  while exp != 0:
+    if (exp and 1) != 0:
+      result *= base
+    exp = exp shr 1
+    base *= base
+
+proc next(s): int =
+  for n in s(): return n
+
+proc powers(m): auto =
+  iterator it(): int{.closure.} =
+    for n in 0 .. <int.high:
+      yield n ^ m
+  return it
+
+iterator filtered(s1, s2): int =
+  var v = next(s1)
+  var f = next(s2)
+  while true:
+    if v > f:
+      f = next(s2)
+      continue
+    elif v < f:
+      yield v
+    v = next(s1)
+
+var
+  squares = powers(2)
+  cubes = powers(3)
+  i = 1
+for x in filtered(squares, cubes):
+  if i > 20:
+    echo x
+  if i >= 30:
+    break
+  inc i