introduce TaskState trait

Used to not require access to the WorkerTask struct outside
the `server` and `api2` module, so it'll be easier to
separate those backup/server/client parts into separate
crates.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

src/lib.rs

@@ -1,3 +1,5 @@
+pub mod task;
+
 #[macro_use]
 pub mod buildcfg;