Add CI - Circle CI

[jumaallan]

Can we include a Continuous Integration like Circle CI to this Repo, to make it easy to build and integrate contributions from external contributors.

[kisese]

@jumaallan thank you for the suggestion and contribution, we would prefer if contributions continue to be done via pull requests as has been happening.

[jumaallan]

@kisese Hi Brian, I have a created a pull request for a few changes. I will also be working on the same in the next couple of days

[kisese]

@jumaallan Noted. The contribution is highly welcome, a polite request would be to focus on any improvements you can add focusing on the payment, checkout and callback experience. With simplicity and readability in mind

[jumaallan]

Great. Working on that. But we can also make the documentation better