Feature: Allow passing arrays of globs

Sometimes it's desired to pass an array of globs instead of just one glob to simplify negation, for example. Right now this isn't possible since glob is the object key in the JSON notation and making it an array will lead to malformed JSON.

There is a proposed solution https://github.com/okonet/lint-staged/pull/188 to create a special syntax to split strings but IMO syntax isn't very user-friendly.

In order to make this change, we'll need to update the config format which will be a breaking change. But before we do that, I'd really like to implement better config validation.

We should use https://github.com/micromatch/micromatch for this one