kable() with kableExtra::kable_styling() duplicates table headings

[ismayc]

The fix is to replace all kable() |> kable_styling() with kbl() |> kable_styling() where kbl() is from the kableExtra package. This has been done for v2, but v1 published at moderndive.com also needs to be updated.

[ismayc]

Addressed with #530