[hp-diff-changes] Implement hands on hp-diff-changes (#112)

# Exercise Review

## Exercise Discussion

Link the exercise discussion issue #105 

## Checklist

- [ ] If you require a new remote repository on the `Git-Mastery`
organization, have you [created a
request](https://github.com/git-mastery/exercises/issues/new?template=request_exercise_repository.md)
for it?
- [ ] Have you written unit tests using
[`repo-smith`](https://github.com/git-mastery/repo-smith) to validate
the exercise grading scheme?
- [X] Have you tested the download script using `test-download.sh`?
- [X] Have you verified that this exercise does not already exist or is
not currently in review?
- [ ] Did you introduce a new grading mechanism that should belong to
[`git-autograder`](https://github.com/git-mastery/git-autograder)?
- [ ] Did you introduce a new dependency that should belong to
[`app`](https://github.com/git-mastery/app)?

Author: FisherSkyi

hands_on/diff_changes.py

@@ -0,0 +1,80 @@
+import os
+
+from exercise_utils.file import create_or_update_file, append_to_file
+from exercise_utils.git import add, init, commit, tag
+
+__requires_git__ = True
+__requires_github__ = False
+
+
+def download(verbose: bool):
+    os.makedirs("things")
+    os.chdir("things")
+    init(verbose)
+    create_or_update_file(
+        "fruits.txt",
+        """
+        apples
+        bananas
+        cherries
+        dragon fruits
+        """,
+    )
+    add(["fruits.txt"], verbose)
+    commit("Add fruits.txt", verbose)
+    append_to_file("fruits.txt",
+                   """
+                   elderberries
+                   figs
+                   """
+    )
+    add(["fruits.txt"], verbose)
+    commit("Add elderberries and figs to fruits.txt", verbose)
+
+    create_or_update_file(
+        "colours.txt",
+        "a file for colours\n",
+    )
+    create_or_update_file(
+        "shapes.txt",
+        "a file for shapes\n",
+    )
+    add(["colours.txt", "shapes.txt"], verbose)
+    commit("Add colours.txt, shapes.txt", verbose)
+
+    tag("v0.9", verbose)
+
+    # Replace the whole contents of fruits.txt
+    create_or_update_file("fruits.txt",
+                   """
+                   apples, apricots
+                   bananas
+                   blueberries
+                   cherries
+                   dragon fruits
+                   figs
+                   """
+    )
+    add(["fruits.txt"], verbose)
+    commit("Update fruits list", verbose)
+
+    append_to_file("colours.txt",
+                    """
+                    blue
+                    red
+                    white
+                    """
+    )
+    add(["colours.txt"], verbose)
+    commit("colours.txt: Add some colours", verbose)
+
+    append_to_file("shapes.txt",
+                   """
+                   circle
+                   oval
+                   rectangle
+                   square
+                   """
+    )
+    add(["shapes.txt"], verbose)
+    commit("shapes.txt: Add some shapes", verbose)