Add tasks for all the new languages

Task/Euler-method/Nim/euler-method.nim

@@ -0,0 +1,13 @@
+import strutils
+
+proc euler(f: proc (x,y: float): float; y0, a, b, h: float) =
+  var (t,y) = (a,y0)
+  while t < b:
+    echo formatFloat(t, ffDecimal, 3), " ", formatFloat(y, ffDecimal, 3)
+    t += h
+    y += h * f(t,y)
+
+proc newtoncooling(time, temp): float =
+  -0.07 * (temp - 20)
+
+euler(newtoncooling, 100.0, 0.0, 100.0, 10.0)