Speedup test suite

Good day, Craig.

Please take a look at this PR

I firstly need only one fix - to make sure on demo mode key is calculated correctly. But next i found that tests are failing and are very slow.

Because it is a better practice to abstract underlying user of API from API itself, so VCR was used to store all the requests. Because for sure we do not want to test actual API behaviour. Only behaviour of a gem. So, now it is more abstract.
And much faster ^_^

```
40.447212s vs 0.183696s
```
Also i moved project to bunder, so requirements and gem version control is much easier.

I would be very appreciated if you are able to review. Please lemme know if you have any questions.