style_lookup: Look up and compute styles
In rsheets/linen: Spreadsheet Data Structures

Work with linen_style objects. This is going to need documentation, but the details are still being worked out.

1	style_lookup(x, ..., idx = NULL)

`x`	An object that can can converted into a `linen_style` object; either the style data itself, or a worksheet or workbook object.
`...`	A set of elements to be extracted. These must be nested with "/" (e.g., "num_fmt/is_date_time"), and can be named (in which case the output is named).
`idx`	optional vector to subset the computed style with