document array export from config file

[Rich-Harris]

As of 0.42, config files can export an array, and all the builds will happen in parallel. This also works with watch mode

[nathancahill]

Important to note in the docs that each config object in the array must have its own instance of any plugins used. Sharing plugin instances across configs will cause unexpected behavior.

[ghost]

Sharing plugin instances across configs will cause unexpected behavior.

Could this be expanded upon just a little? I haven't seen any unexpected behavior with minify or license under basic use, though I'm only using them with a single import from within just one config file (pre- and post-0.42 release) to roll 6 bundles.

[nathancahill]

Some plugins might work, others might not. I think rollup-plugin-uglify with it's custom output options was where I noticed the issue. When a plugin reads from the Rollup config object, it will overwrite that value until the last config in the array.

[ghost]

Thanks for expanding. I'm using the new array syntax to output bundles and using uglifiy with harmony. Looks good to me. Not sure if our set-ups differ, but I'm using the technique left in your PR to create the minis. Was very pleased by being able to remove a dev dependency with that pull. 💯