Extend `Grid` with column options

[adamkudrna]

Originally discussed in #146:

Yes, now it may be mistaken for the usual grid component that exists in other UI libraries. The “usual grid” also has a different way of usage: you would need cells or grid items to wrap around the content you want to put in the grid. That's because how the grid is built: with flexbox. However, that's not our case. We want a next-generation grid component using the right tool for the job: the grid layout. Imagine extending the Grid component in the future like this:

<Grid items="3" size="1fr">
  <div>…</div>
  <div>…</div>
  <div>…</div>
</Grid>

It could go further with non-repetitive layouts like this:

<Grid columns="minmax(200px, 300px) 1fr">
  <div>…</div>
  <div>…</div>
</Grid>

Originally posted by @adamkudrna in #146 (comment)

[adamkudrna]

Inspiration in Orbit by Kiwi: https://orbit.kiwi/components/grid/react/