0.0.1 release: third-party and project support

* Third-party support (accounts receivable and accounts payable)
* Project support
* django 1.5 and 1.6 compatability
* "quick start" documentation in README
* 100% code coverage on unit tests
* ledger entries generate unique id
* ledger iterators can be truth-tested for emptiness
* separation of the interface from the storage implementation