Describe the bug
When called with a slice, JustItem returns a Single that sends multiple values. However the documentation (and the name) suggests that a Single should send one value. There appears to be no way to send a slice as a single value, which is very counterintuitive!

To Reproduce
The following code demsonstrates the issue: (also on Go playground)

package main

import (
    "fmt"

    "github.com/reactivex/rxgo/v2"
)

func main() {
    data := []int{1, 2, 3}
    observable := rxgo.JustItem(data)

    for x := range observable.Observe() {
	    fmt.Println("Item:", x.V)
    }
}

Produces output:

Item: 1
Item: 2
Item: 3

Expected behavior
Output:

Item: [1 2 3]

Additional context
The problem appears to be caused by the send function (item.go:75) which switches on the type of each item.