A lots of updates related to the test suite.

* Add minitest as test framework of the gem
* Add VCR to record the request answers
* Add Turn to pretify our output
* Update the Rake Task test to load minitests suite
* Change the way the leetchi key is loaded. It now use a path instead
of the key itself.
* Moved the resources outside of the resource folder. For better
architecture.

Still got to write some tests on the new features.

Ref: #3 #4 #6
Update tests suite

* Update README to reflect tests suite changes
* Remove the test folder. It's not needed yet. It could be nice to
readd it later when we need unit tests.
* Move the VCR calls outside of the it methods
* Move the let calls outside of the it methods to limit code duplication
* Update wallet spec
* Update card spec
Add tests for the beneficiaries error codes
Add contributions spec.

Test both create and get methods
Add Withdrawal specs.

It still fails on the create method codes since the user has no money
on his account. I've got to find a way to make this work.
Add the Cards spec.

Test Create, Get and Delete method.
It made clear that there is an error on the delete method. Will need to
be fixed.
Add minitest to Gemfile + update README.md to include the ruby versions
Merge pull request #12 from Leetchi/Tests-Rewirte

Update all of the test suite.