* CombinableTransactions now separated out.
* CombinableTransactions are now size-aware when being executed, and will automatically split into batches for execution if they are too big.
* New MarketInstructionBuilder approach - each market type can now have its own way of building instructions for common operations.
* Extended mechanism for combining instructions.
* Fixed Account's calculations of deposits and borrows.
* Added net_assets to Account.
* Groups now maintain loaded RootBanks, not just PublicKeys of them.
* Fixed simple market-maker's calculation of position sizes.
Geoff Taylor