Add tasks for all the new languages

Task/Set/Sidef/set-1.sidef

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+class Set(*set) {
+
+    method init {
+        var elems = set;
+        set = Hash.new;
+        elems.each { |e| self += e }
+    }
+
+    method +(elem) {
+        set{elem} = elem;
+        self;
+    }
+
+    method del(elem) {
+        set.delete(elem);
+    }
+
+    method has(elem) {
+        set.has_key(elem);
+    }
+
+    method ∪(Set that) {
+        Set(set.values..., that.values...);
+    }
+
+    method ∩(Set that) {
+        Set(set.keys.grep{ |k| k ∈ that } \
+                    .map { |k| set{k} }...);
+    }
+
+    method ∖(Set that) {
+        Set(set.keys.grep{|k| !(k ∈ that) } \
+                    .map {|k| set{k} }...);
+    }
+
+    method ^(Set that) {
+        var d = ((self ∖ that) ∪ (that ∖ self));
+        Set(d.values...);
+    }
+
+    method count { set.len }
+
+    method ≡(Set that) {
+        (self ∖ that -> count.is_zero) && (that ∖ self -> count.is_zero);
+    }
+
+    method values { set.values }
+
+    method ⊆(Set that) {
+        that.set.keys.each { |k|
+            k ∈ self || return false;
+        }
+        return true;
+    }
+
+    method to_s {
+        "Set{" + set.values.map{|e| "#{e}"}.sort.join(', ') + "}"
+    }
+}
+
+class Object {
+    method ∈(Set set) {
+        set.has(self);
+    }
+}