Feature/show columns

[gro1m]

Another attempt of implementing show columns based on #160.

Related issue:

• Markdown & Ignore Files #79

[gro1m]

@aconrad Is there still interest in this feature? Because the rebuild that it needs first affects all future development and involves a lot of chore work. Some changes in the meantime that the other request was open necessitated some rework. And I appreciate the time it takes to review these things, but I would also like that this feature is implemented in a somewhat timely manner.

[gro1m]

This is why I only did for the show and not for the diff command yet and also no tests for the moment in order to get your feedback on priority.

[aconrad]

@gro1m thanks so much for looking into this, I really appreciate it. I think it could be useful to have this feature since it was requested. Although honestly I don't know how common it is of a request. There aren't many columns to begin with.

But if we were to implement this in the least intrusive way, could we just pass the list of columns to render to the template? I understand it would be a waste of computation because we'd be gathering data for all columns and only rendering the ones we care at the end. But I feel it would be an easier implementation to begin with. What do you think?