Fix tests for interactive testing within RStudio or Positron (thanks @robitalec).
New exo_blame() exercise to practice finding who added a specific line with git blame.
New exo_log_deleted_file() exercise to practice finding a deleted file with git log -- <path>.
New exo_log_deleted_line() exercise to practice finding a deleted line with git log --S<string> or git log --R<regex>.
New exo_revparse() exercise to practice parsing ancestry references with git rev-parse.
New exo_worktree() exercise to practice git worktree.
Add instructions with "switch" and "restore" alongside "checkout" equivalents (#30).