Complete support for v3 API Endpoints

- add support for Catalogs endpoint
- add support for Version endpoint
- change string representation of Resource type to type[name]
- add type classes for Catalog, Edge to represent relationship
  between Resources
- add basic unit tests for new types
Add README section on catalogs endpoint, pep8 fix
fix test_connect_api_v3
Merge pull request #22 from juliushaertl/feature-apiv3

Complete support for v3 API Endpoints