Now use a right-recursive `Tuple2` instead a flat `Product`.
Do not include labels.  As a result, dropped shapeless dependency.
Updated to 2.13
Dropped tests as scalameter not supported in 2.13.

Squashed commit of the following:

commit 3e1148c780bf9d8a9ec86a1e6e0ef6e675d8074f
Author: Luciano Joublanc <luciano@joublanc.com>
Date:   Thu Feb 14 10:41:46 2019 +0000

    Update documentation

    Use new tupled representation.

commit 8350cc36
Author: Luciano Joublanc <luciano@joublanc.com>
Date:   Mon Feb 11 10:08:57 2019 +0000

    Update docs and annotations

commit 1e13124c
Author: Luciano Joublanc <luciano@joublanc.com>
Date:   Fri Feb 8 16:57:38 2019 +0000

    Scala 2.13 cross build.
    Remove scalameter as there's no 2.13 support.

commit 40a10f49
Author: Luciano Joublanc <luciano@joublanc.com>
Date:   Thu Feb 7 17:14:35 2019 +0000

    Implement copyToArray

commit f4aeca12
Author: Luciano Joublanc <luciano@joublanc.com>
Date:   Thu Jan 24 13:59:45 2019 +0000

    Change dir structure

commit f807f91a
Author: Luciano Joublanc <luciano@joublanc.com>
Date:   Thu Jan 24 13:51:01 2019 +0000

    Use recursive Tup for columns