Kanboard API returns int (ID) on success and false (bool) on failure
for create operations. Add IntOrFalse type that handles both cases
and update CreateTask, CreateComment, CreateTag, CreateTaskFile, and
CreateTaskLink to use it.
- GetAllTaskLinks: retrieve all links for a task
- CreateTaskLink: create link between two tasks
- RemoveTaskLink: delete a task link
- TaskScope.GetLinks and LinkTo for fluent API
- Link types include "blocks", "is blocked by", etc.
- Comprehensive test coverage
