Add command line switch for executing arbitrary forms

[arichiardi]

I was working on a cider issue: clojure-emacs/cider#1751

But then got stuck as there is no way to require from the command line. I think I saw someone asking kind of a similar thing on Slack, so maybe we can add some flag that enables to execute a form in boot.user before or even without having to rely on build.boot?

Would you guys be open to a patch?

[micha]

@arichiardi Sure, that sounds great to me!

[oahner]

On the topic of adding a flag to execute arbitrary forms, it would be useful to have a similar flag that executes the content of a file rather than just the string, effectively bypassing the shebang issue on Windows.