Pre-allocate capacity for slice with make

---

examples/slice-pre-allocate/slice_pre_allocate.go

package main

import (
    "fmt"
)

func main() {
    dwarfs := make([]string, 0, 10)
    fmt.Println(dwarfs)
    fmt.Println(len(dwarfs))
    fmt.Println(cap(dwarfs))

    dwarfs = append(dwarfs, "Happy")
    fmt.Println(dwarfs)
    fmt.Println(len(dwarfs))
    fmt.Println(cap(dwarfs))

    dwarfs = append(dwarfs, "Grumpy", "Sleepy")
    fmt.Println(dwarfs)
    fmt.Println(len(dwarfs))
    fmt.Println(cap(dwarfs))
}

[]
0
10
[Happy]
1
10
[Happy Grumpy Sleepy]
3
10