Initial Support for Work items V2 API
 Support for V2 in createWorkItem
 bumped default API version to 1.0-preview.1
 Improved response parsing, it was failing if an error was returned
Support HTTP proxies in tests
Support for work item API changes in version 1.0-preview.1
  Still compatible with 1.0-preview.1
  Fixed unit V1 unit tests
  Added unit tests for V2
Support for V2 changes
 work item methods support both V1 and V2
 added new methods only available in V2
Merge pull request #21 from tspascoal/master

Add support for work item API 1.0-preview.2 version