0.06:
  - Improve search function.

0.05:
  - Implement ticket identity mapping in Ticket class now.
  - Loading the same ticket id multiple times with the same connection object should return identical objects.
  - fix memory leaking of ticket objects.

0.04:
  - Implement ticket deletion
  - Implement ticket refresh method
  - Implement ticket search
  - The ticket class methods are changed and it is incompatible with previous versions.

0.03:
  - Implement ticket status changes
  - Implement ticket history

0.02:
  - Implement a top-level Net::Redmine API
  - Implement ticket identity mapping using Net::Redmine APIs

0.01:
  _ Implement Ticket creating and loading.
