Add proof of concept for generic mkcamp_command.

[racke]

This by no means a complete implementation. Please tell me if you like this idea.
Our use case in local-config:

after_templates_mkcamp_command:carton install

[jonjensen]

I like this idea a lot. The only thing I think it needs is to use pushd() instead of chdir(), as we don't want to mess with the global cwd state. Could you make that change?

[racke]

Sure, it will just take a while.

[jonjensen]

Stefan, I'd still like to get this merged if you're using a after_templates_mkcamp_command feature. Are you game to use pushd instead?

[racke]

Sure, that is fine for me.

[jonjensen]

@racke So ... are you going to contribute a revised patch? I thought that's what you meant when you said "Sure, it will just take a while." before.

[racke]

Yes, I'm going to contribute a revised patch.