Add hspec-contrib with retryWith-function

Fix this https://github.com/hspec/hspec/pull/200.
Add hspec-contrib package and retryWith function.
Change hspec-core's exposed module for above package.


You can import `Test.Hspec.Core` instead of `Test.Hspec.Core.Type`.   This way we do not have to expose `Test.Hspec.Core.Type`.