consider a readline integration

I don't want to pull in a ton of crap and maybe that'd mean moving grol the main into a sub dir or different package to keep the library go.mod clean/small

there are many of them, need to pick something appropriate (and small!)

https://github.com/openengineer/go-repl
https://github.com/peterh/liner

and more:

https://pkg.go.dev/search?q=readline
