Make Client an interface instead of a struct

This makes it easier to maintain per-institution hacks that start
interacting with each other if you try to do them all in the same client
code. This commit also breaks out the existing Vanguard hack into its
own Client implementation.

cmd/ofx/detect_settings.go

@@ -126,12 +126,13 @@ func tryProfile(appID, appVer, version string, noindent bool) bool {
 		fmt.Println("Error creating new OfxVersion enum:", err)
 		os.Exit(1)
 	}
-	var client = ofxgo.BasicClient{
-		AppID:       appID,
-		AppVer:      appVer,
-		SpecVersion: ver,
-		NoIndent:    noindent,
-	}
+	var client = ofxgo.GetClient(serverURL,
+		&ofxgo.BasicClient{
+			AppID:       appID,
+			AppVer:      appVer,
+			SpecVersion: ver,
+			NoIndent:    noindent,
+		})
 
 	var query ofxgo.Request
 	query.URL = serverURL

cmd/ofx/util.go

@@ -12,12 +12,13 @@ func newRequest() (ofxgo.Client, *ofxgo.Request) {
 		fmt.Println("Error creating new OfxVersion enum:", err)
 		os.Exit(1)
 	}
-	var client = ofxgo.BasicClient{
-		AppID:       appID,
-		AppVer:      appVer,
-		SpecVersion: ver,
-		NoIndent:    noIndentRequests,
-	}
+	var client = ofxgo.GetClient(serverURL,
+		&ofxgo.BasicClient{
+			AppID:       appID,
+			AppVer:      appVer,
+			SpecVersion: ver,
+			NoIndent:    noIndentRequests,
+		})
 
 	var query ofxgo.Request
 	query.URL = serverURL
@@ -27,5 +28,5 @@ func newRequest() (ofxgo.Client, *ofxgo.Request) {
 	query.Signon.Org = ofxgo.String(org)
 	query.Signon.Fid = ofxgo.String(fid)
 
-	return &client, &query
+	return client, &query
 }