indicators and navigation of changed lines

[tksoh]

Several editors/IDE out there have indicator on the line number area and scroll bar, to mark the lines that has been added/deleted/modified. This let us quickly identify the changes during editing, so we don't have to waste time hunting for them.

Hopefully this feature can be added to nedit-ng soon.

To speed things up, perhaps we can add feature that let us navigate through the changes like the diff tool such as kdiff3, etc.

[tksoh]

Also, if and when we have the support for VCS like git, we can display the changes based on 'git diff' if the file is part of git repo.