Added Symfony Options Resolver component to composer.json
AbstractTransactor now uses an OptionsResolver to enforce and validate options passed to the transact method
Fixed BC break introduced by adding OptionsResolver
NMI CardTransactor now uses OptionsResolver to manage options
PaymentsXpress transactor now uses options resolver
Merge pull request #9 from tyler-sommer/feature/options-resolver

Use OptionsResolver to validate options passed to Transaction->transact