[Checkout.com] Implementation of all functions with test cases

[ravirocx]

Implementation of :

• Authorize/3
• Capture/3
• Purchase/3
• void/2
• refund/3

and its supportive private functions

[codecov-io]

Codecov Report

Merging #167 into dev will decrease coverage by 6.98%. The diff coverage is 77.1%.

@@            Coverage Diff             @@
##              dev     #167      +/-   ##
==========================================
- Coverage   77.33%   70.34%   -6.99%     
==========================================
  Files          14       15       +1     
  Lines         375      489     +114     
==========================================
+ Hits          290      344      +54     
- Misses         85      145      +60

Impacted Files	Coverage Δ
lib/gringotts/response.ex	100% <ø> (ø)	:arrow_up:
lib/mix/new.ex	0% <0%> (ø)	:arrow_up:
lib/gringotts/gateways/wire_card.ex	0% <0%> (ø)
lib/gringotts/gateways/stripe.ex	0% <0%> (ø)	:arrow_up:
lib/gringotts/credit_card.ex	100% <100%> (ø)	:arrow_up:
lib/gringotts.ex	100% <100%> (ø)	:arrow_up:
lib/gringotts/gateways/authorize_net.ex	97.56% <100%> (ø)	:arrow_up:
lib/gringotts/gateways/paymill.ex	100% <100%> (ø)	:arrow_up:
lib/gringotts/gateways/trexle.ex	100% <100%> (ø)	:arrow_up:
lib/gringotts/gateways/global_collect.ex	100% <100%> (ø)	:arrow_up:
... and 17 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 73ea35e...6ff6f73. Read the comment docs.