add calculate_short_proceeds_up

[dpaiton]

Resolved Issues

Partially addresses #29 and #21

Description

These are steps towards implementing a parity implementation of open short as well as targeted short.

• Add a function to calc short proceeds & round up, which is used in the Open Short flow.
• Modifies calculate short proceeds down to look more like the up version.

Since these functions are implemented on State, we preferentially use State member variables (e.g. vault_share_price) instead of passing arguments.

The short proceeds is given by:

$$ P_{\text{short}}(\Delta y) = \tfrac{\Delta y \cdot c_{1}}{c_{0} \cdot c} + \tfrac{\Delta y}{c} \cdot \phi_{f} - \Delta z(\Delta y) $$