func (tx *Tx) SetOptions(options *Options) {
	tx.options = options
	if options.isMultiOp {
		tx.Start(options.multiOpSource)
	}
}
SetOptions sets the Tx options
package microstellar
import (
	"net/http"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
	"github.com/stellar/go/build"
	"github.com/stellar/go/clients/horizon"
	"github.com/stellar/go/xdr"
)
type Tx struct {
	client        *horizon.Client
	networkName   string
	network       build.Network
	fake          bool
	options       *Options
	builder       *build.TransactionBuilder
	payload       string
	submitted     bool
	response      *horizon.TransactionSuccess
	isMultiOp     bool                        
	ops           []build.TransactionMutator  
	sourceAccount string
	err           error
}
func NewTx(networkName string, params ...Params) *Tx {
	var network build.Network
	var client *horizon.Client
	fake := false
	switch networkName {
	case "public":
		network = build.PublicNetwork
		client = horizon.DefaultPublicNetClient
	case "test":
		network = build.TestNetwork
		client = horizon.DefaultTestNetClient
	case "fake":
		network = build.TestNetwork
		client = horizon.DefaultTestNetClient
		fake = true
	case "custom":
		if len(params) < 1 {
			logrus.Errorf("missing parameters for custom network, connecting to testnet")
			return NewTx("test")
		}
		url, ok1 := params[0]["url"]
		passphrase, ok2 := params[0]["passphrase"]
		if !(ok1 && ok2) {
			logrus.Errorf("missing url or passphrase, connecting to testnet")
			return NewTx("test")
		}
		network = build.Network{Passphrase: passphrase.(string)}
		client = &horizon.Client{
			URL:  url.(string),
			HTTP: http.DefaultClient,
		}
	default:
		network = build.TestNetwork
		client = horizon.DefaultTestNetClient
	}
	return &Tx{
		networkName: networkName,
		client:      client,
		network:     network,
		fake:        fake,
		options:     nil,
		builder:     nil,
		payload:     "",
		submitted:   false,
		response:    nil,
		isMultiOp:   false,
		ops:         []build.TransactionMutator{},
		err:         nil,
	}
}