Support Vector arguments by combining multiple identical options into a single Vector

Hi there,
it would be nice if there is a possibility to support Vector arguments out of the box. Like
```julia
@main function main(a; b::Vector{Int})
    # ...
end
```
and call it with `myscript "a" --b 1 --b 2 --b 5` so that `b=Int[1,2,5]`


EDIT: ArgParse.jl apparently has support for it. See https://carlobaldassi.github.io/ArgParse.jl/latest/arg_table.html#Available-actions-and-nargs-values-1