Show changes in various forms

[Byron]

Run something like a git status and git show, implementing differences between tree - tree - index - worktree.

Assorted Tasks

• [x] diff trees with trees
• [ ] a complete enough index implementation (see #293 )
• [ ] an understanding on how worktrees work (also consider git worktree) in conjunction git-index (see #301)
• [ ] diffing of worktree -> index -> tree