Add support for task tags

Based on properties named `tag.<tag>` as already documented

taskchampion/src/lib.rs

@@ -34,9 +34,7 @@ mod utils;
 
 pub use config::{ReplicaConfig, ServerConfig};
 pub use replica::Replica;
-pub use task::Priority;
-pub use task::Status;
-pub use task::{Task, TaskMut};
+pub use task::{Priority, Status, Tag, Task, TaskMut};
 
 /// Re-exported type from the `uuid` crate, for ease of compatibility for consumers of this crate.
 pub use uuid::Uuid;