#20 allow to proceed with some unsolved levels

[Anonymous]

Sometimes you're stuck at a level. It's frustrating
not to be able to continue the game and get back to
that level later.

It would be extremely nice if you could continue to
the next level even without solving current one.

Of course it should be limited, so only, say, 5 levels
could be left unsolved behind. Or even progressively,
you start with possible one unsolved, after solving 12
th you can have two, after 24th three, 36th - four and
after 48th you can have five unsolved levels.

Of course reaching 60th level would bring you back to
first unsolved level, not "Congratulations" page. :)