Suggestion: --command / -c attribute

[Slava]

If I want to schedule something which will take sometime can't close session or write some boring boilerplate like:

bash -c 'wait-on mysite.com && do something' & disown

And because I relate on status from wait-on I can't use bg or wait. But if wait-on had --command attribute which will run in daemonized/background mode I don't even need them:

wait-on condition -c 'do something'

As a proposed solution for: #16