Set the default minting provider and profile in config.ini via %Mint

While digging into "dzil new" I thought it was tiresome to continually execute "dzil new -P Author::APOCAL Foo::Bar::Baz" and wanted to set it as a default somewhere. I looked at the docs and it seems like there's no way to do it?

This pull request adds a new stash, %Mint that allows you to specify the default in the config.ini file. I think this is sensible enough for me and was very simple to implement, yay!

It's missing tests as I'm not sure where to begin, ha! Thanks again for looking at this :)