Return Value On Setup For Easy Setup

Changed to return XCGLogger back from setup allowing you to do setup when creating the log instance globally. Swift does not allow expressions in global code so your can't do the setup right when instantiating it. This change makes it so you don't need to put it in your applicationDidLaunch you can put it anywhere you like. Since my applicationDidLaunch was not in swift yet, this made it easier to adopt XCGLogger. Now to instantiate and setup, just do this anywhere:

let log = XCGLogger.defaultInstance().setup(logLevel:.Debug, showLogLevel:false, showFileNames: false, showLineNumbers:false, writeToFile:nil)