Merge pull request #11 from devton/master

Added calcule_installments method into PagarMe::Util class
Move calculate_installments to Transaction class.
Add installments support to subscription charge method.
Bump version.
Remove Gemfile.lock from repository.
Remove error validation in library
Implement boleto refund
Remove repeated code.
Add Card model.
Let users create transaction with card model.
Bump to version 1.9.6.
Bump to 1.9.7.
Remove wrong tests.