Add nicer tests

[joestrong]

The current tests aren't doing much

Mainly the API endpoint needs to be mocked so the endpoint isn't a part of the test

I'm happy for phpspec to be replaced by phpunit etc

[royalmitten]

Will look into this over the weekend!
We should be able to do this with the current PHPSpec implementation, or do you prefer using PHPUnit?

[joestrong]

@royalmitten I just started adding more tests with phpspec, so I'm happy to stick with that now. Also I've started using Guzzle's mocking tools to mock the API endpoints.

Any additional tests, or changes to the tests are welcome. I think the code should be throwing its own exceptions instead of Guzzle exceptions, so I think that could be a good improvement to the code and the tests.

[mannion007]

PR here #20

Refactored some code to decouple from Guzzle, making testing with phpspec much cleaner. In the future you could easily add integration tests that do use the RetroAchievements adapter to make real requests if you want to.

That's my last PR for Hacktoberfest =)