Add an alternative syntax escaping than `$`

[pdeffebach]

I've been using a kind of peculiar workflow where I just @eval inside a main() function to have a Revise-like script workflow. Unfortunately this means I can't use $ inside that @eval block. Would be nice to have an alternative syntax to $, since $ is so widely used everywhere else for escaping.

[pdeffebach]

The answer is to un-deprecate cols.