func NewClient(apiKey, apiSecret string) (c *client) {
	return NewClientWithCustomTimeout(apiKey, apiSecret, (30 * time.Second))
}
NewClient return a new HitBtc HTTP client
package hitbtc
import (
	"encoding/json"
	"errors"
	"fmt"
	"io/ioutil"
	"net/http"
	"net/url"
	"strings"
	"time"
)
type client struct {
	apiKey     string
	apiSecret  string
	httpClient *http.Client
}
var (
	lastRequest       time.Time
	RequestsPerSecond float64                         = 10
	BeforeRequest     func(method, path string) error = nil
	AfterRequest      func()                          = nil
)
func init() {
	BeforeRequest = func(method, path string) error {
		elapsed := time.Since(lastRequest)
		if elapsed.Seconds() < (float64(1) / RequestsPerSecond) {
			time.Sleep(time.Duration((float64(time.Second) / RequestsPerSecond) - float64(elapsed)))
		}
		return nil
	}
	AfterRequest = func() {
		lastRequest = time.Now()
	}
}