When Stripe announced earlier this year that it had picked up another $600 million in funding, it said one big reason for the funding was to expand its API-based payments services into more geographies. Today the company is coming good on that plan in the form of some M&A. Stripe is acquiring Paystack, a startup out of Lagos, Nigeria that, like Stripe, provides a quick way to integrate payments services into an online or offline transaction by way of an API. (We and others have referred to it in the…