Create and use some testing API:

* Ledger::pointer
  createGenesisLedger(std::uint64_t start_amount_drops,
                      RippleAddress const& master);

* std::pair<RippleAddress, RippleAddress> createAccount();

* void
    makePayment(RippleAddress const& from, RippleAddress const& to,
                std::uint64_t amountDrops, Ledger::pointer const& ledger);