Show changes in various forms

[Byron]

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

Assorted Tasks

• diff trees with trees
• diff blobs with blobs (using imara-diff)
• a complete enough index implementation (see gix-index towards 1.0 #293 )
• an understanding on how worktrees work (also consider git worktree) in conjunction git-index (see gix-worktree and gix-index (checkout, status, commit) #301)
• diffing of worktree -> index -> tree

[Byron]

Superseded by #301 .