[FEATURE] Diff command to compare against local changes

[dnaka91]

Is your feature request related to a problem? Please describe.

Depending on the program used, it's often easy to forget about the linked dotfile and make some changes through the application's UI, then later unintentionally resetting those changes when calling bombadil link.

Therefore, it would be great to have a new command to compare the local files against the template output.

Describe the solution you'd like

A new diff command, that first renders all the templates, then compares them against the currently linked files and drops into a diff (like git diff). Could be either on the terminal, or send the diffs to a default application, similar to diffing with Git.

This might be extended into making the link command run a diff by default, then showing the diffs and asking to continue before overwriting all the files.

Describe alternatives you've considered

Additional context

[dnaka91]

Might be related to #138

[oknozor]

This would be a nice addition indeed.
I think sending diff to an external pager application preferable.

The easiest way to implement this would be to use imara-diff
which produces standard git diff output. From there we would be able to use existing git pagers such as git-delta etc.