Add logging handler to Log utility

[ZevEisenberg]

#When I Log.error(...), I don't just want to print that to the console. I also want to log it to my crash reporter, analytics, etc. An easy way to accommodate this is to provide a static var loggingHandler: ((String) -> Void)? that you can set to a closure that passes you the logging string, and you can do whatever you want with it.