add InsertSmtpSetting method
add tests for method InsertSmtpSetting
add ReplaceSmtpSetting method
select and append the correct nodes
reformat
add tests for ReplaceSmtpSetting and add additional tests for InsertSmtpSetting
update readme for CustomErrorSettings
Revert "update readme for CustomErrorSettings"

This reverts commit 61b5e784d74d7ad6244b473a6e1ebf0e0ce88a85.
Merge pull request #6 from lightyeare/smtp-tranform

Add transform for smtp mailSettings