implementation Zaim::Client#update with specs

 * update payment/income/transfer
implementation Zaim::Client#delete with specs

 * delete payment/income/transfer
implementation Zaim::Client#category with specs
implementation Zaim::Client#genre with specs
implementation Zaim::Client#account with specs
write README.md
update gemspec
add travis-ci target 1.9.2 / 1.9.3