Still TODO:

- Early: Foreign column checking
- Result validation with schema
- Warnings: Additional or missing columns

Also more WIP for XLSX conversion.

Squashed commit of the following:

commit f85fcabe
Merge: 35e621d0 4e2a676f
Author: Daniel <d.hornung@indiscale.com>
Date:   Fri Apr 26 12:51:40 2024 +0200

    Merge branch 'f-table-json-data-schema' into f-convert-xlsx-to-json

commit 35e621d0
Author: Daniel <d.hornung@indiscale.com>
Date:   Fri Apr 26 12:37:22 2024 +0200

    WIP: XLSX table reader

commit 03bd9f91
Merge: 84f13721 5700bb20
Author: Daniel <d.hornung@indiscale.com>
Date:   Wed Apr 24 15:15:35 2024 +0200

    Merge branch 'dev' into f-convert-xlsx-to-json

commit 84f13721
Author: Daniel <d.hornung@indiscale.com>
Date:   Tue Apr 23 18:05:57 2024 +0200

    WIP: XLSX reader

commit 2f20561b
Author: Daniel <d.hornung@indiscale.com>
Date:   Fri Apr 19 11:27:56 2024 +0200

    WIP: XLSX reader.

commit 4f616ada
Author: Daniel <d.hornung@indiscale.com>
Date:   Fri Apr 19 11:27:21 2024 +0200

    MAINT: Refactored helper functions.

commit e93984c0
Author: Daniel Hornung <d.hornung@indiscale.com>
Date:   Thu Apr 18 09:02:53 2024 +0200

    WIP: XLSX reader

Note: It could be that the real issue is just a problem of reference resolution order..

Tests now also test for handling of invalid data.