Add tasks for all the new languages

Task/Averages-Mode/Sidef/averages-mode-1.sidef

@@ -0,0 +1,6 @@
+func mode(array) {
+    var c = Hash.new;
+    array.each{|i| c{i} := 0 ++};
+    var max = c.values.max;
+    c.keys.grep{|i| c{i} == max};
+}

Task/Averages-Mode/Sidef/averages-mode-2.sidef

@@ -0,0 +1,2 @@
+say mode([1, 3, 6, 6, 6, 6, 7, 7, 12, 12, 17]).join(' ');
+say mode([1, 1, 2, 4, 4]).join(' ');

Task/Averages-Mode/Sidef/averages-mode-3.sidef

@@ -0,0 +1,3 @@
+func one_mode(arr) {
+    arr.max_by{|i| arr.count(i)};
+}