Adds new Punto Pagos gateway

[ldlsegovia]

I made a gateway to integrate https://www.puntopagos.com (a Chilean service for payments) https://www.puntopagos.com/Home/Integracion https://github.com/PuntoPagos/documentacion

Form the contributing section:

Include test/fixtures.yml if the gateway’s test credentials are shareable (recommended)

the key and secret are not shareable. You need to contact with puntopagos to get sandbox access.

Must have unit tests and functional remote tests

• Unit

• Remote

Remote tests for a gateway should cover all supported transaction methods (auth, purchase, capture, refund, void, verify, store and scrub) and validate critical response formats such as charge amounts

Punto Pagos works like PaypalExpressGateway. Because of this, the generated template did not fit. So, I improvised a bit and copied from that gateway.

Your code should support all the Ruby versions and ActiveSupport versions we have enabled on Travis CI

Done.

No new gem dependencies will be accepted

No new dependencies added.

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Finally, a working example: