func (s *store) Add(p index.Path) error {
	s.Lock()
	defer s.Unlock()
	k := fmt.Sprintf("%v", p)
	s.m[k] = append(s.m[k], time.Now().UTC())
	return s.store.Persist(&s.m)
}
Add implements Store.
package history
import (
	"fmt"
	"sync"
	"time"
	"tchaik.com/index"
)
type Store interface {
	Add(index.Path) error
	Get(index.Path) []time.Time
}
func NewStore(path string) (Store, error) {
	m := make(map[string][]time.Time)
	s, err := index.NewPersistStore(path, &m)
	if err != nil {
		return nil, err
	}
	return &store{
		m:     m,
		store: s,
	}, nil
}
type store struct {
	sync.RWMutex
	m     map[string][]time.Time
	store index.PersistStore
}