calls.go
func (c *CallService) MakeCall(from string, to string, u *url.URL) (*Call, error) {
	data := url.Values{}
	data.Set("From", from)
	data.Set("To", to)
	data.Set("Url", u.String())
	return c.Create(context.Background(), data)
}
func (c *CallService) MakeCall(from string, to string, u *url.URL) (*Call, error) {
	data := url.Values{}
	data.Set("From", from)
	data.Set("To", to)
	data.Set("Url", u.String())
	return c.Create(context.Background(), data)
}
// MakeCall starts a new Call from the given phone number to the given phone
// number, dialing the url when the call connects. MakeCall is a wrapper around
// Create; if you need more configuration, call that function directly.