Fee reclamation and rebates

[jjgonecrypto]

No description provided.

[jacko125]

@justinjmoses

Potentially on settle() if there is a difference on the dest synth price after (M minutes), we can issue or burn the difference of the two prices against the dest synth instead of diverting the difference to the FeePool.

Ie, Exchange 100 sUSD to 1 sETH (@ $100 ETH) , the user would get 1 sETH

If the price after 3 minutes was higher for ETH at $102.7 (2.7 % higher), then we can burn the extra amount of sETH that the trader received, to equal the actual price of $102.7 after M minutes.

The trader should have gotten actually 100 sUSD / 102.7 = 0.9737098345 sETH minus any fees.

Inversely, if any rebates are due on settlement after 3 Minutes, it would work the same way, we can then issue more of the dest synth to cover the price shift after 3 Minutes.

The trader still has to execute into the position and signal that they would be locked into the trade and not be able to move / transfer / exchange until after 3M when it settles.

[jjgonecrypto]

Actually that's a much better solution @jacko125. That also solves the concerns I had about the Fee Pool being drained. @brian0641 had mentioned the idea of minting sUSD on rebates - but I hadn't joined the dots. I'll update this PR.