[global-collect] Layout, docs improvements and code refactors (#111)

[global-collect] Layout, docs and code refactor
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New features
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Risk, AVS, CVS fields added in `Response` struct!

Layout, docs
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* `credo` issues resolved.
* Corrected `amount` in examples
* Ran the elixir 1.6 code formatter
  - Used sigils in mocks

Code refactors
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* Removed unnecessary functions
  - Reduced arity of `add_money`
* Refactored Timex usage
* Removed a test on `validate_config` as it is already tested.