api: Add go files

I know this is a huge commit, but I can't be bothered to check
this in part by part.

api/smtp_owner_confirm_hex.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"bytes"
+	"net/smtp"
+	"os"
+)
+
+type ownerConfirmHexPlugs struct {
+	Origin     string
+	ConfirmHex string
+}
+
+func smtpOwnerConfirmHex(to string, toName string, confirmHex string) error {
+	var header bytes.Buffer
+	headerTemplate.Execute(&header, &headerPlugs{FromAddress: os.Getenv("SMTP_FROM_ADDRESS"), ToAddress: to, ToName: toName, Subject: "Please confirm your email address"})
+
+	var body bytes.Buffer
+	templates["confirm-hex"].Execute(&body, &ownerConfirmHexPlugs{Origin: os.Getenv("ORIGIN"), ConfirmHex: confirmHex})
+
+	err := smtp.SendMail(os.Getenv("SMTP_HOST"), smtpAuth, os.Getenv("SMTP_FROM_ADDRESS"), []string{to}, concat(header, body))
+	if err != nil {
+		logger.Errorf("cannot send confirmation email: %v", err)
+		return errorCannotSendEmail
+	}
+
+	return nil
+}