Add way to toggle background light or dark

There is maybe a better place for this.

I'm a VimL beginner, I hope my code is correct. At home, it works.

.vimrc

@@ -75,6 +75,19 @@
 " General {
 
     set background=dark         " Assume a dark background
+
+    " Allow to trigger background
+    function! ToggleBG()
+        let s:tbg = &background
+        " Inversion
+        if s:tbg == "dark"
+            set background=light
+        else
+            set background=dark
+        endif
+    endfunction
+    noremap <leader>bg :call ToggleBG()<CR>
+
     " if !has('gui')
         "set term=$TERM          " Make arrow and other keys work
     " endif