Documentation of topics

[olivroy]

Some concepts of gt are valuable to learn as a whole

I believe it would be interesting to have that for other parts of gt

• [ ] Specifying columns
• [ ] Specifying rows
• [ ] locale (awaiting #1593)
• [ ] date and time styles
• [ ] palette (what is a valid palette) (split from data_color()
• [x] locations #1658
• [ ] Specifying a function. (for summary rows, grand summary rows

Probably others?

Remove long form info from functions and includes links everywhere

Maybe implement

stop_input_type(

   what = cli::format_inline("a {.topic [cells_*()](locations-helper)}"
)

Instead of adding long docs that cell_source_notes() cannot be used in tab_footnote(), generate an informative error? Can;t a dd a footnote that targets source notes, see location-helper for possible choices.

Add a check_column_classes_are_valid in the fmt_*() functions.

Review how from_column() is documented. maybe create info_from_column()

Turns out `@family supports md links, so can be useful to create links

#' @family Other [location helper][location-helper] function