Avoid logging warnings

[h4cc]

I found some logs from this library, because of this code:

https://github.com/operable/fumanchu/search?utf8=%E2%9C%93&q=Logger&type=

Could we remove that Logger entry and integrate such warnings in the API ?

Or at least prefix the message with something that could be filtered, like this:
Logger.warn(~s[fumanchu: template:#{line}:#{col}: tag end mismatched: "}}}"])