Add tasks for all the new languages

Task/Levenshtein-distance/Sidef/levenshtein-distance-1.sidef

@@ -0,0 +1,15 @@
+func lev(s, t) is cached {
+
+    s.is_empty && return t.len;
+    t.is_empty && return s.len;
+
+    var s1 = s.ft(1);
+    var t1 = t.ft(1);
+
+    s[0] == t[0] ? __FUNC__(s1, t1)
+                 : 1+[
+                        __FUNC__(s1, t1),
+                        __FUNC__(s,  t1),
+                        __FUNC__(s1, t )
+                     ].min;
+}

Task/Levenshtein-distance/Sidef/levenshtein-distance-2.sidef

@@ -0,0 +1,11 @@
+func lev(s, t) {
+    var d = [@(0 .. t.len), s.len.of {[_]}...]
+    for i,j in (^s ~X ^t) {
+        d[i+1][j+1] = (
+            s[i] == t[j]
+                ? d[i][j]
+                : 1+Math.min(d[i][j+1], d[i+1][j], d[i][j])
+        )
+    }
+    d[-1][-1]
+}

Task/Levenshtein-distance/Sidef/levenshtein-distance-3.sidef

@@ -0,0 +1,2 @@
+say lev(%c'kitten', %c'sitting');               # prints: 3
+say lev(%c'rosettacode', %c'raisethysword');    # prints: 8