Improved library

Made numerous improvements as I'm a fan of the aesthetics of the alert views.

1. Added a `SCLAlertViewResponder` class that allows the use of `.Close()`, `.setTitle(String)` and `.setSubTitle(String)` upon instantiating a new `SCLAlertView`.

2. Added convenience functions for each style of alert. Such as `SCLAlertView().showSuccess(self, title: "", subTitle: "")` which is purely for readability. Assumes 2.0 duration.

3. Added the option in `.showTitle()` to change the 'Done' button to whatever you wish under the `completeText` attribute. It is optional and defaults to the original 'Done'.

4. Updated README to reflect new changes and polished up a few mistakes. Also cleaned up the code to look slightly more readable and syntactically beautiful.

Good work. Look forward to seeing this develop a bit. Try to get it on Cocoapods too. This has helped me learn Swift a bit more too.