add settings API

samples/settings-test.lua

@@ -1,18 +1,13 @@
 function on_resume()
   local s1 = {
-    key1 = "value1",
-    key2 = "value2",
+    key1 = "123",
+    key2 = "val ue   2",
   }
 
   settings:set_kv(s1)
 
   local s2 = settings:get_kv()
 
-  ui:show_text("key1="..s2.key1.." ".."key2="..s2.key2)
+  ui:show_text("key1=\""..s2.key1.."\" ".."key2=\""..s2.key2.."\"")
 end
 
-function on_settings()
-  local s = settings:get_kv()
-
-  ui:show_dialog("Settings", "key1="..s.key1.." ".."key2="..s.key2)
-end