func SetDefaultBytesPool(bp *BytesPool) {
	defaultBytesPool = bp
}
SetDefaultBytesPool change default pool options
package gxbytes
import (
	"sync"
)
type BytesPool struct {
	sizes  []int  
	slots  []sync.Pool
	length int
}
var defaultBytesPool = NewBytesPool([]int{512, 1 << 10, 4 << 10, 16 << 10, 64 << 10})
func NewBytesPool(slotSize []int) *BytesPool {
	bp := &BytesPool{}
	bp.sizes = slotSize
	bp.length = len(bp.sizes)
	bp.slots = make([]sync.Pool, bp.length)
	for i, size := range bp.sizes {
		size := size
		bp.slots[i] = sync.Pool{New: func() interface{} {
			buf := make([]byte, 0, size)
			return &buf
		}}
	}
	return bp
}