Implement user's config as init file and add directory into package.path

Create the user's config init file if lite user's config directory does
not exists.

No longer use the awkward package.searchers but instead add user's
config dir at the end of package path.

src/api/system.c

@@ -8,6 +8,7 @@
 #include "api.h"
 #include "rencache.h"
 #ifdef _WIN32
+  #include <direct.h>
   #include <windows.h>
 #endif
 
@@ -314,6 +315,25 @@ static int f_get_file_info(lua_State *L) {
 }
 
 
+static int f_mkdir(lua_State *L) {
+  const char *path = luaL_checkstring(L, 1);
+
+#ifdef _WIN32
+  int err = _mkdir(path);
+#else
+  int err = mkdir(path, S_IRUSR|S_IWUSR|S_IXUSR|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH);
+#endif
+  if (err < 0) {
+    lua_pushboolean(L, 0);
+    lua_pushstring(L, strerror(errno));
+    return 2;
+  }
+
+  lua_pushboolean(L, 1);
+  return 1;
+}
+
+
 static int f_get_clipboard(lua_State *L) {
   char *text = SDL_GetClipboardText();
   if (!text) { return 0; }
@@ -397,6 +417,7 @@ static const luaL_Reg lib[] = {
   { "window_has_focus",    f_window_has_focus    },
   { "show_confirm_dialog", f_show_confirm_dialog },
   { "chdir",               f_chdir               },
+  { "mkdir",               f_mkdir               },
   { "list_dir",            f_list_dir            },
   { "absolute_path",       f_absolute_path       },
   { "get_file_info",       f_get_file_info       },