Use Scratch.jl for update messages

[Datseris]

From a discussion on Slack that will be forever lost, it is better to use https://github.com/JuliaPackaging/Scratch.jl to display update messages instead of the current pipeline with touch. Stefan Karpinski said that

We really don’t want people modifying package code in place 😢

and also cited other related problems, while Elliot Saba further commended that the approach will be impossible in the future:

We’re eventually going to make packages read-only.

Elliot thankfully pointed out that the replacement is easy:

https://github.com/JuliaPackaging/Scratch.jl , Basically, instead of using the DIR macro, you would use the get_scratch macro, that's the only change. But you get a lot of benefits, including that it will work even if your package is included in PackageCompiler output. The scratch directory can be cleared, if for example the package is uninstalled then reinstalled later. The user can also manually clear it.

[Datseris]

@Libbum keep this in mind as well for Agents.jl

[Libbum]

Cool. This is a decent change. Will add it to the list—thanks.