Merge pull request #191 from korczis/master-clean

Fix GoodData::Project#add_user
Merge pull request #192 from korczis/master-clean

Improved Tests
Merge branch 'master' of https://github.com/gooddata/gooddata-ruby into master-clean
Merge pull request #193 from korczis/master-clean

Simplify
Merge branch 'master' of https://github.com/gooddata/gooddata-ruby into master-clean