Add tasks for all the new languages

Task/Mandelbrot-set/Nim/mandelbrot-set.nim

@@ -0,0 +1,20 @@
+import complex
+
+proc mandelbrot(a): Complex =
+  for i in 0 .. <50:
+    result = result * result + a
+
+iterator stepIt(start, step, iterations) =
+  for i in 0 .. iterations:
+    yield start + float(i) * step
+
+var rows = ""
+for y in stepIt(1.0, -0.05, 41):
+  for x in stepIt(-2.0, 0.0315, 80):
+    if abs(mandelbrot((x,y))) < 2:
+      rows.add('*')
+    else:
+      rows.add(' ')
+  rows.add("\n")
+
+echo rows