Add tasks for all the new languages

Task/Left-factorials/Nim/left-factorials.nim

@@ -0,0 +1,26 @@
+import iterutils, bigints
+
+proc lfact: iterator: BigInt =
+  result = iterator: BigInt =
+    yield 0.initBigInt
+    var
+      fact = 1.initBigInt
+      sum = 0.initBigInt
+      n = 1.initBigInt
+    while true:
+      sum += fact
+      fact *= n
+      n += 1
+      yield sum
+
+echo "first 11:\n  "
+for i in lfact().slice(last = 10):
+  echo "  ", i
+
+echo "20 through 110 (inclusive) by tens:"
+for i in lfact().slice(20, 110, 10):
+  echo "  ", i
+
+echo "Digits in 1,000 through 10,000 (inclusive) by thousands:"
+for i in lfact().slice(1_000, 10_000, 1_000):
+  echo "  ", ($i).len