* 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.
* This is a big change that touched most files in the project.
* Library code is now an actual package, in /mango.
* Pure .py files used for shared code - easier to edit/debug, and should ease move to installable package later.
* Removed many notebooks. The remaining notebooks are useful 'display'/'show' notebooks for investigating Mango objects.
* More tests! The test story is now much improved, but more unit tests are still needed.
* There's now a Makefile for project operations.
Geoff Taylor