Feature request: allow preprocessing the output

[visrosa]

This might be outside the scope of this software, but it would be useful to set custom tools to run on the output before display by ov, ideally tied to view modes.

Colored output (and preprocessing in general) can already be achieved by common pipes, e.g. pygmentize file | ov, or by using something like bat that calls ov as a pager.

But being able to tell ov itself to run those has three advantages I can see:

1. ov remains aware of the file it is displaying rather than just saying "stdin"
2. when using ov --exec it would allow for coloring the ouput while still maintaining separate stdin and stderr
3. allows the user to set up custom preprocessing for edge cases, such as the small edits necessary to get fstab displaying nicely as a table I described in #269

[noborus]

Thank you for the issue. I'll think about it carefully.