func WithLogger(l logger) func(rpc *EthRPC) {
	return func(rpc *EthRPC) {
		rpc.log = l
	}
}
WithLogger set custom logger
package ethrpc
import (
	"io"
	"net/http"
)
type httpClient interface {
	Post(url string, contentType string, body io.Reader) (*http.Response, error)
}
type logger interface {
	Println(v ...interface{})
}
func WithHttpClient(client httpClient) func(rpc *EthRPC) {
	return func(rpc *EthRPC) {
		rpc.client = client
	}
}