Experimental #saveoptions command

Add a #saveoptions extended command, to allow saving configuration
settings from within the game. This is still highly experimental,
and gives plenty of warnings before asking to overwrite the file.

Lack of option saving is one of the biggest complaints new players
have, so this should help with it.  More experienced players with
highly customized config file should not use this feature, as it
completely rewrites the file, removing all comments and non-config
lines.

src/nhlua.c

@@ -631,7 +631,7 @@ nhl_get_config(lua_State *L)
     int argc = lua_gettop(L);
 
     if (argc == 1) {
-        lua_pushstring(L, get_option_value(luaL_checkstring(L, 1)));
+        lua_pushstring(L, get_option_value(luaL_checkstring(L, 1), TRUE));
         return 1;
     } else
         nhl_error(L, "Wrong args");