Fix package header

Otherwise package.el's `package-buffer-info` will raise an error
complaining that Package lacks a header.

Add vc-jj package definition

Implement vc-jj-working-revision

Implement vc-jj-state

Implement vc-jj-registered

Add setup instructions for project.el integration

Implement responsible-p in terms of vc-jj-root

That way, we can use the same logic for other functions, like checking
if a file is tracked by jj.

Fix checkout-model implementation

Implement vc-jj-responsible-p

So that we can start dog-fooding vc-jj.el. With this function, so that
vc-dir should work for the vc-jj backend.

Rename vc-jujutsushi.el to vc-jj.el

This is to align with the convention of naming the vc backend file as
vc-<name>.el.

Add some low hanging fruits

Add package definition

First pass at `jj-dashboard'

It basically just writes the output of the commands to a buffer. Next we
need to add sections and overlays to annotate the output.

First pass at `jj-describe'

It works. However there are several UX issues to address. The first one
is that one needs to manually save the buffer and close in order to
yield back to jj to store the describe. We should define a mode so that
we can bind C-c C-c to record the description. The mode can be set if
the buffer ends in ".jjdescription".

🤟 This description was written from Emacs using jujutushi.el 🤟

Stub  jj-dashboard

First pass at vc-jj-create-repo

register the vc-jj backend

Add list of vc functions to implement

Add jujutsushi-vc.el

Add jujutsuhi-project.el integration