allow task setters to return error values

lib/src/result.rs

@@ -1,10 +1,11 @@
+// TODO: make true = 1, false = 0, error = -1
 /// A result combines a boolean success value with
 /// an error response.  It is equivalent to `Result<bool, ()>`.
 /// cbindgen:prefix-with-name
 /// cbindgen:rename-all=ScreamingSnakeCase
 #[repr(C)]
 pub enum TCResult {
-    True,
-    False,
-    Error,
+    Error = -1,
+    False = 0,
+    True = 1,
 }