Fixing some issues

[nastari]

Hey man, i fixed and made audits in some points on the contract about the gas optimization,
I didn't make every flow in the contract, but i think it is possible to pass a view about... for example, the wasted returned's parameters on the "deliver" function could be refact.

https://whimsical.com/empiricus-SdRZGk2pbdC2DXCquKd8rb