Add tasks for all the new languages

Task/Middle-three-digits/Nim/middle-three-digits.nim

@@ -0,0 +1,16 @@
+import math
+
+proc middleThreeDigits(i): auto =
+  var s = $abs(i)
+  if s.len < 3 or s.len mod 2 == 0:
+    raise newException(ValueError, "Need odd and >= 3 digits")
+  let mid = s.len div 2
+  return s[mid-1..mid+1]
+
+const passing = @[123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345]
+const failing = @[1, 2, -1, -10, 2002, -2002, 0]
+
+for i in passing & failing:
+  var answer = try: middleThreeDigits(i)
+    except ValueError: getCurrentExceptionMsg()
+  echo "middleThreeDigits(",i,") returned: ",answer