Block list builders

Build a generic block container. This would be named div, but that clashes with prelude's div.

Build a generic inline container. This would be named span, but that clashes with prelude's span.

Build a level 1 header.

Build a level 2 header.

Build a level 3 header.

Build a level 4 header.

Build a level 5 header.

Colspans seem to be quite important for controlling table layout, so much so that a version of SimpleTable which takes a [ColSpan] seemed in order.

Build a Str using a values's Show instance.