Update changelog and tests for new path printing logic

CHANGELOG.md

@@ -4,6 +4,18 @@
 
 Added support for Solidity.
 
+### Display
+
+When difftastic is invoked with two file paths, it will now truncate
+the path shown to the shared common parts. This is particularly
+helpful when using difftastic with mercurial.
+
+```
+$ difft dir1/foo/bar.py dir2/foo/bar.py
+foo/bar.py -- Python
+...
+```
+
 ## 0.46 (released 31st March 2023)
 
 ### Command Line Interface

tests/cli.rs

@@ -160,3 +160,13 @@ fn git_style_arguments_rename() {
     let predicate_fn = predicate::str::contains("Renamed");
     cmd.assert().stdout(predicate_fn);
 }
+
+#[test]
+fn drop_different_path_starts() {
+    let mut cmd = Command::cargo_bin("difft").unwrap();
+
+    cmd.arg("sample_files/dir_before/clojure.clj")
+        .arg("sample_files/dir_after/clojure.clj");
+    let predicate_fn = predicate::str::contains("dir_after/clojure.clj").not();
+    cmd.assert().stdout(predicate_fn);
+}