[TEST] Previous test cases were using the functionality being tested.

The previous version of these tests was using `get_address` just like the code being tested. It's better to check if the code in question has actually been able to correctly find the public key (which means it also found the correct private key.)
Merge pull request #154 from justmoon/new_seed_test

Improve Seed#get_key test cases.
Update docs
Update owner_funds
Merge pull request #155 from ripple/develop

Update documentation, fix owner_funds not updated in orderbook