lib: Add _get_{int,string}() APIs

- add integer and string version of the APIs,
- Also Refine the APIs, return value to indicate the setting existance
  and a new param to return the value of the setting.
- add their lua bindings as well, in lua binding the return value nil
  indicates that the setting is not defnied.
- Add corresponding C and lua tests as well.
- Add a few handy debug msgs.

modules/module-lua-scripting/api/api.c

@@ -1485,8 +1485,59 @@ get_boolean (lua_State *L)
 
   if (s)
   {
-    gboolean value = wp_settings_get_boolean (s, setting);
-    lua_pushboolean (L, value);
+    gboolean value = 0;
+    if (wp_settings_get_boolean (s, setting, &value))
+      lua_pushboolean (L, value);
+    else
+      lua_pushnil (L);
+  }
+  else
+    lua_pushnil (L);
+  return 1;
+}
+
+static gboolean
+get_string (lua_State *L)
+{
+  const char *setting = luaL_checkstring (L, 1);
+  const char *m = NULL;
+
+  if (lua_type (L, 2) == LUA_TSTRING)
+    m = luaL_checkstring (L, 2);
+
+  g_autoptr (WpSettings) s = wp_settings_get_instance (get_wp_core (L), m);
+
+  if (s)
+  {
+    const gchar *value = NULL;
+    if (wp_settings_get_string (s, setting, &value))
+      lua_pushstring (L, value);
+    else
+      lua_pushnil (L);
+  }
+  else
+    lua_pushnil (L);
+  return 1;
+}
+
+static gboolean
+get_int (lua_State *L)
+{
+  const char *setting = luaL_checkstring (L, 1);
+  const char *m = NULL;
+
+  if (lua_type (L, 2) == LUA_TSTRING)
+    m = luaL_checkstring (L, 2);
+
+  g_autoptr (WpSettings) s = wp_settings_get_instance (get_wp_core (L), m);
+
+  if (s)
+  {
+    gint64 value = 0;
+    if (wp_settings_get_int (s, setting, &value))
+      lua_pushinteger (L, value);
+    else
+      lua_pushnil (L);
   }
   else
     lua_pushnil (L);
@@ -1521,6 +1572,8 @@ apply_rule (lua_State *L)
 static const luaL_Reg settings_methods[] = {
   { "get_boolean", get_boolean },
   { "apply_rule", apply_rule },
+  { "get_string", get_string },
+  { "get_int", get_int },
   { NULL, NULL }
 };