Add tasks for all the new languages

Task/Greatest-common-divisor/Nim/greatest-common-divisor-1.nim

@@ -0,0 +1,5 @@
+proc gcd_recursive(u, v: int64): int64 =
+    if u %% v != 0:
+        result = gcd_recursive(v, u %% v)
+    else:
+        result = v

Task/Greatest-common-divisor/Nim/greatest-common-divisor-2.nim

@@ -0,0 +1,9 @@
+proc gcd_iterative(u1, v1: int64): int64 =
+  var t: int64 = 0
+  var u = u1
+  var v = v1
+  while v != 0:
+      t = u
+      u = v
+      v = t %% v
+  result = abs(u)

Task/Greatest-common-divisor/Nim/greatest-common-divisor-3.nim

@@ -0,0 +1,35 @@
+proc gcd_binary(u1, v1: int64): int64 =
+  var t, k: int64
+  var u = u1
+  var v = v1
+  u = abs(u)
+  v = abs(v)
+  if u < v:
+      t = u
+      u = v
+      v = t
+  if v == 0:
+    result = u
+  else:
+    k = 1
+    while (u %% 2 == 0) and (v %% 2 == 0):
+      u = u shl 1
+      v = v shl 1
+      k = k shr 1
+    if (u %% 2) == 0:
+      t = u
+    else:
+      t = -v
+    while t != 0:
+      while (t %% 2) == 0:
+        t = t div 2
+      if t > 0:
+        u = t
+      else:
+        v = -t
+      t = u - v
+    result = u * k
+
+echo ("GCD(", 49865, ", ", 69811, "): ", gcd_iterative(49865, 69811), " (iterative)")
+echo ("GCD(", 49865, ", ", 69811, "): ", gcd_recursive(49865, 69811), " (recursive)")
+echo ("GCD(", 49865, ", ", 69811, "): ", gcd_binary   (49865, 69811), " (binary)")