Expose ReadlineWithDefault

[terwey]

Hi,

I would like to use ReadlineWithDefault(what string) from the Readline library.
https://github.com/abiosoft/readline/blob/master/readline.go#L258-L261

Currently only Readline() is exposed but I want to give the user a default value.

What is the best approach? Extend ishell and send a PR?

Thanks.

[terwey]

Never mind, I see it's in the master branch: v2...master