(Soft-)deprecate `column_map()`?

[jmobrien]

column_map() uses the old endpoint (e.g. #267), sometimes creates issues (e.g. #283), and has an established replacement (extract_colmap()). Should we go ahead and deprecate it?

If so, should we soft-deprecate w/a warning pointing to the new function, or go ahead and deprecate fully (throwing a similarly-worded error)?

Leaning towards the latter since I think the older version really doesn't offer anything uniquely useful, so most all users probably want the newer maps.

[juliasilge]

Yeah, let's go straight to deprecate_warn() with this. Good idea.

[jmobrien]

Okay, I was using the language inadequately here, but thanks for the link. deprecate_warn() makes sense.