show undo diff (#3213)

Exposes undo operations via the C API, and uses those to show a (new, differently formatted) diff before committing the undo.

taskchampion/lib/src/lib.rs

@@ -65,7 +65,7 @@ ffizz_header::snippet! {
 /// ## Pass by Pointer
 ///
 /// Several types such as TCReplica and TCString are "opaque" types and always handled as pointers
-/// in C. The bytes these pointers address are private to the Rust implemetation and must not be
+/// in C. The bytes these pointers address are private to the Rust implementation and must not be
 /// accessed from C.
 ///
 /// Pass-by-pointer values have exactly one owner, and that owner is responsible for freeing the
@@ -153,7 +153,7 @@ pub use workingset::*;
 
 pub(crate) mod types {
     pub(crate) use crate::annotation::{TCAnnotation, TCAnnotationList};
-    pub(crate) use crate::kv::{TCKVList, TCKV};
+    pub(crate) use crate::kv::TCKVList;
     pub(crate) use crate::replica::TCReplica;
     pub(crate) use crate::result::TCResult;
     pub(crate) use crate::server::TCServer;