Lots of small improvements

- creating projects
- adding/removing tags to tasks
- get workspace by id (to get is_organization)
- continuing implementation of async Tasks
- serialization flags for AsanaProject
- constructors for AsanaProject
Small fixes

- Move the IsFaulted code to the correct place
- Support serialization
- AsanaTag constructor
- AsanaTask fixes
- Refresh() for workspace
- CreateWorkspaceTag
Make IsOrganization nullable

Makes it possible to determine whether it was originally fetched or not
Implemented Delete functions and missing Update ones and other changes

Other changes:
- Cast operators
- Constructors
- Alternative (more universal) way of calling Get functions by Type
AsanaFunctions for the new Get

Needs improvement of code (duplication, not DRY), but since it compiles
to text it doesn't really matter for performance.
Merge pull request #18 from niieani/asynctasks

Lots of small improvements