added charge resource

[Oluwatemilorun]

So I added the charge resource that gives access to endpoints of charge

Paystack.charge.card() to charge with card Paystack.charge.bank() to charge with bank Paystack.charge.authorizationCode() to charge with authorization code Paystack.charge.submitPin() to submit pin after charge with card Paystack.charge.submitOTP() to submit OTP after charge

Also did a check for the required parameters for each endpoint and maintained the Promise returns. Created a test for it...but not sure it will work with the sane pattern of other test. Tested with node test/charge.js