Add static methods to differentiate message from message templates.

Ideally, everything Serilog methods take are message templates, which is great! But more often than not, we do have to end up writing simple text messages, like 

    Log.Information("That is complete!");

The problem with this, is that message templates are cached internally, and hence, adds pressure and reduces performance, being a different string each time. Using message templates is the best practice, but for the simplest of the situations, this ends up being counter-intuitive. 

**Solution**: Pass all the text without parameters into the same template "{_}" so that it always uses that specific cached template, and pass the text as a parameter, thereby also having the ability to pass simple strings without the performance hit.