I've had these on `<leader>k` and `<leader>j` since the early days, but
those mappings no longer feel logical to me. It seems that `[b` and `]b`
are unbound, so I decided to bind these to buffer switching, for the
rare times when I need it.

Eventually I'll probably remove one or the other set depending on what I
end up sticking with.

Mapping to make it easier to insert a pre-defined signature in emails.

Sometimes I don't have any line comments to make and can go ahead and
accept or reject a change immediately.

In those cases, I want `PrrApprove` and `PrrReject` to be available in
any file type buffer, not just in *.prr buffers.

Additionally, those two commands should automatically do `PrrStart` if
it hasn't been executed manually before, like we already do with
`PrrComment`.

This variable isn't necessary. The same effect can be accomplished with
the try-catch.

Ensure that diff corrections are applied in a `vimdiff` context, where
we haven't run `:diffthis` manually.

Change the diff background colours from their defaults to make the text
in the foreground easier to read.

If the Prr session hasn't been started yet, do so automatically when
running `PrrComment`. This lets me comment directly on a line without
having to worry about starting the Prr review beforehand.

Now that I see the code and my earlier TODO, I think I could probably
have made it work without the `s:active` flag. Will have to try removing
it and testing whether that works.

Set up custom insert mappings for GitHub Copilot based on what makes
sense to me and inspired by the existing i_^x Vim completion mappings.

Add a new mapping to quickly comment on a line.

If `PrrStart` hasn't been run yet, we should error and stop execution so
we don't insert newlines and start insert mode in the current buffer.

Eventually, we should set it up so `PrrStart` is called automatically
from `PrrComment` if it hasn't been already.