Module flow

The module is a thin wrapper around the functionality that converts between shares and assets, using the Balancer pool's stable math logic. The module also gives protection against reentrancy while inside the view context, where state cannot be modified. The state being unmodifiable is accomplished by VaultReentrancyLib.sol, which tries to purposefully trigger the actual reentrancy guard, expecting it to immediately revert when the reentrancy flag is mutated in a (read-only) view context. From the length of the revert data, it is possible to differentiate between a revert due to actual reentrancy or an attempt to modify state in a view context.