Add tasks for all the new languages

Task/Stack/Phix/stack-1.phix

@@ -0,0 +1,23 @@
+sequence stack = {}
+
+procedure push(object what)
+    stack = append(stack,what)
+end procedure
+
+function pop()
+    object what = stack[$]
+    stack = stack[1..$-1]
+    return what
+end function
+
+function empty()
+    return length(stack)=0
+end function
+
+?empty()                -- 1
+push(5)
+?empty()                -- 0
+push(6)
+?pop()                  -- 6
+?pop()                  -- 5
+?empty()                -- 1