func NewLimiter(d time.Duration) *Limiter {
	return &Limiter{delay: d}
}
NewLimiter returns a Limiter that will wait for the specified duration between Wait calls.
package ncbi
import (
	"encoding/xml"
	"io"
	"net/http"
	"net/url"
	"strings"
	"sync"
	"time"
)
var client = http.Client{Timeout: 10 * time.Second}
func SetTimeout(d time.Duration) {
	client.Timeout = d
}
type Limiter struct {
	m     sync.Mutex
	delay time.Duration
	next  time.Time
}