check_excel_range: Check that a specific list element is an excel range string
In a-maldet/readall: Read FWF, DSV, EXCEL And SAS Files

Assumes non-zero length.

1	check_excel_range(obj, attr, err_h, allow_na = FALSE, allow_null = FALSE)

`obj`	The list object, that should be checked
`attr`	A string holding the name of the list element, that should be checked.
`err_h`	An error handler.
`allow_na`	Are `NA` values allowed?
`allow_null`	A logical, defining whether the argument is allowed to be `NULL`.