Implement --dry-run command line argument

[AlexDaniel]

So that it will be possible to see which tasks are going to be executed.

[Xliff]

@AlexDaniel,

I'd be happy to implement this.
Do you have any idea how you would prefer to pass parameters to separate tasks?

[AlexDaniel]

I was thinking about a global flag in MAIN.

[Xliff]

Sure. But here's the way I was thinking about implementing it:

Take global flag from main.
Pass it to tasks.
If it finds :$dry_run as truthy, then print task name and return.

Sure, it could probably use headers and such to indicate that a run is being dried, but that could be done in either MAIN or execute().