func (cs Changes) Swap(i, j int) {
	cs[i], cs[j] = cs[j], cs[i]
}
Swap is part of sort.Interface.
package agollo
type ChangeType string
const (
	ChangeTypeAdd    ChangeType = "add"
	ChangeTypeUpdate ChangeType = "update"
	ChangeTypeDelete ChangeType = "delete"
)
type Change struct {
	Type  ChangeType
	Key   string
	Value interface{}
}
type Changes []Change
func (cs Changes) Len() int {
	return len(cs)
}