Support string message

[elnn]

Our logger class will look like this:

private val log = LoggerFactory.getLogger(this.getClass);
log.value(tag, value);
log.log(level, msg);
log.debug(msg);
log.info(msg);
log.error(msg);

[yunseong]

• Because LoggerFactory is a name used in another project, I think it would better to use 'RemonLogger'
• We need to update the document to cover this issue since it is a design change.

[elnn]

We did not resolve this issue on time. Move to the next iteration.

[elnn]

Close by #58