`soft_delete_columns()` potentially misleading api for users

[HoffsMH]

If the function only adds a single column to a table then might we want to change the name to
soft_delete_column?

I didn't want to open up multiple PRs at a time but if I have the go ahead I have a branch ready.

I think that a change like this actually has some dangers.
Since the only files that this function will be called in are migration files and it is generally frowned upon to edit migration files after checking them into source control.

If the api changes it should be backwards compatible and only the documentation should change with it.

I would consider deprecation warnings for the plural version but I wonder if that would be detrimental in terms of encouraging developers to edit migration files.

Feedback appreciated but not expected after all it is just a naming issue! 😄

[bryanjos]

I think I left it open just in case we added something else. I almost thought about removing it completely since it doesn't do much