Rename exercises dir

Name it instead "topics" so it won't be
strange if some topics included "exercises" directory.

topics/git/solutions/branch_01_solution.md

@@ -0,0 +1,20 @@
+## Branch 01 - Solution
+
+```
+cd some_repository
+echo "master branch" > file1
+git add file1
+git commit -a -m "added file1"
+git checkout -b dev
+echo "dev branch" > file2
+git add file2
+git commit -a -m "added file2"
+```
+
+Verify:
+
+```
+git log (you should see two commits)
+git checkout master
+git log (you should see one commit)
+```

topics/git/solutions/commit_01_solution.md

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+## Git Commit 01 - Solution
+
+```
+mkdir my_repo && cd my_repo
+git init
+echo "hello_commit" > file
+git add file
+git commit -a -m "It's my first commit. Exciting!"
+git log
+```

topics/git/solutions/squashing_commits.md

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+## Git - Squashing Commits - Solution
+
+
+1. In a git repository, create a new file with the content "Mario" and commit the change
+
+```
+git add new_file
+echo "Mario" -> new_file
+git commit -a -m "New file"
+```
+
+2. Make change to the content of the file you just created so the content is "Mario & Luigi" and create another commit
+
+```
+echo "Mario & Luigi" > new_file
+git commit -a -m "Added Luigi"
+```
+
+3. Verify you have two separate commits - `git log`
+
+4. Squash the two commits you've created into one commit
+
+```
+git rebase -i HEAD~2
+```
+
+You should see something similar to:
+
+```
+pick 5412076 New file
+pick 4016808 Added Luigi
+```
+
+Change `pick` to `squash`
+
+
+```
+pick 5412076 New file
+squash 4016808 Added Luigi
+```
+
+Save it and provide a commit message for the squashed commit
+
+### After you complete the exercise
+
+Answer the following:
+
+* What is the reason for squashing commits? - history becomes cleaner and it's easier to track changes without commit like "removed a character" for example. 
+* Is it possible to squash more than 2 commits? - yes