Add prompt if arguments are empty

[fxrs]

Hey,

I'd like to propose this change to add an user prompt if no arguments were given.
This gives a convenient option for requests while also preventing filling the shell history with every request.

I typically use ctrl-r to retrieve a previous rusty command, but to make a new request, I need to clear the arguments. Executing rusty commands with arguments should not be affected.

Both cargo fmt and cargo clippy ran successfully from what I can tell. Commit allows fast-forward merging onto main branch.

Please review and let me know if you have any comments or suggestions.

Cheers,
Felix

[fxrs]

This also allows reading from file (rusty < test.txt) as well as running it on a selection in vim (eg. make selection, :'<,'>w ! rusty).

[zahidkhawaja]

Thanks, @fxrs! Great idea.