Ok, here's the foot rig.

Quite messy,15 IK SC and 1 RP solver, 100 unamed groups but you just click on foot control behind the heel.
You'll see attribute Foot_Thoes_Curl-->drag middle mouse button in negative to curl toes under.

The foot is not done I didnt have time to finish it-->note when you rotate Foot control around X axies it rotates the whole foot but not around the heel down to the toes.

Anyway, you shouldnt have any problems curling the thoes down.

I hope I helped, note me if you have any suggestion or a problem I would be glad to help or hear your opinion!