Add simple investment requests/responses

This is lacking (at least) parsing the list of securities frequently
sent with investment statements

common.go

@@ -1,6 +1,7 @@
 package ofxgo
 
 import (
+	"errors"
 	"github.com/golang/go/src/encoding/xml"
 )
 
@@ -11,6 +12,22 @@ type Message interface {
 	// it's unmarshaled to ensure the request or response is valid
 }
 
+type Status struct {
+	XMLName  xml.Name `xml:"STATUS"`
+	Code     Int      `xml:"CODE"`
+	Severity String   `xml:"SEVERITY"`
+	Message  String   `xml:"MESSAGE,omitempty"`
+}
+
+func (s *Status) Valid() (bool, error) {
+	switch s.Severity {
+	case "INFO", "WARN", "ERROR":
+		return true, nil
+	default:
+		return false, errors.New("Invalid STATUS>SEVERITY")
+	}
+}
+
 type BankAcct struct {
 	XMLName  xml.Name // BANKACCTTO or BANKACCTFROM
 	BankId   String   `xml:"BANKID"`
@@ -25,3 +42,9 @@ type CCAcct struct {
 	AcctId  String   `xml:"ACCTID"`
 	AcctKey String   `xml:"ACCTKEY,omitempty"` // Unused in USA
 }
+
+type InvAcct struct {
+	XMLName  xml.Name // INVACCTTO or INVACCTFROM
+	BrokerId String   `xml:"BROKERID"`
+	AcctId   String   `xml:"ACCTID"`
+}