add --clean to remove old generated binaries from the cache

[natefinch]

No description provided.

[zmackie]

@natefinch If this isn't claimed, I'd like to take it on.
Questions:

1. Would this be a flag intended to be run on its own, or could it be included with any other command? If the latter, would it run before or after the command in question? If the former, is this a command similar to showVersion or mageInit that would get stuck in this if chain: https://github.com/magefile/mage/blob/master/mage/main.go#L91 ?
2. How do you think this should interact with Keep or is that command orthogonal?

[natefinch]

Awesome, thanks!

So.... ideally I'd like to refactor the command-ish flags so they are required to be run only by themselves. As much as it might be handy to run mage --clean foo bar, the combinatorics become crazy as more commands are created.

So, let's say, starting with this command, if -clean is set, we'll bail if fs.NArgs() > 0 or if fs.NFlags() > 1. I.e. bail if the user specified any other flags or positional args.

And then we can do a separate PR to make -version and -init work the same way.

[natefinch]

This is done as stated above