Various changes, see details of this PR ...

* Attempt to require only required and not whole gooddata
* Fixed Auth Command [https://github.com/korczis/gooddata-ruby/commit/83a8898bfb33c71254aaba7290369686d2c561c5]
* Few Lines of Documentation [https://github.com/korczis/gooddata-ruby/commit/b5efe9a6290d653d6dbf3b97817d4b760b6b5107]
* One class per file, naming convention ClassName => class_name.rb [https://github.com/korczis/gooddata-ruby/commit/540c76ba87230ddcf75ebace102b2a0b4391b68c]
* More compact way to require all files in same dir [https://github.com/korczis/gooddata-ruby/commit/213fb3e01cec2b2d67d3ac7872827b6998f03757, https://github.com/korczis/gooddata-ruby/commit/b72b7f1826f79fe68a4a4a985d6b779db8ae8a33]
* Testable GLI Commands [https://github.com/korczis/gooddata-ruby/commit/4366665241dae2050b2dc8cf6e0d672c09d46f29]


For CI status see [this link](https://travis-ci.org/korczis/gooddata-ruby)