Add the ability to optionally trim messages

[yaronya]

We're using the logger to send outputs of bash commands, and sometimes those commands emit empty messages that doesn't fall under this rule (i.e, they still contain newlines, tabs and etc.) so we need to trim the message before this check.

I think it'd be great to have support for an option to have the log messages trimmed before they're evaluated and sent.
Is this something you'll be willing to add? I'd be glad to open a quick pull request for it 😃