`is_range()`

tests whether or not an Excel formula is a range.
A formula like `A1`

is a range, whereas a formula like `MAX(A1,2)`

is not.
Formulas are not evaluated, so it returns `FALSE`

for formulas that would
eventually resolve to arrange (e.g. `INDEX(A1:A10,2)`

) but that are not
immediately a range.

## Examples

```
x <- c("A1", "Sheet1!A1", "[0]Sheet1!A1", "A1,A2", "A:A 3:3", "MAX(A1,2)")
is_range(x)
#> [1] TRUE TRUE TRUE TRUE TRUE FALSE
```