Add tasks for all the new languages

Task/Combinations/Phix/combinations.phix

@@ -0,0 +1,13 @@
+procedure comb(integer pool, needed, done=0, sequence chosen={})
+    if needed=0 then    -- got a full set
+        ?chosen         -- (or use a routine_id, result arg, or whatever)
+        return
+    end if
+    if done+needed>pool then return end if -- cannot fulfil
+    -- get all combinations with and without the next item:
+    done += 1
+    comb(pool,needed-1,done,append(chosen,done))
+    comb(pool,needed,done,chosen)
+end procedure
+
+comb(5,3)