Improved readability
Improved readability

- Add pattern matching with the where clause in the if statement improving clean syntax and improvements of Swift 2.
- Change () for Void in every closure to improve the clarity in the code and following the guidelines of using closures in Swift.
- Add two typealias to the closures in the function setObjectForKey() to improve reusability and readibility in the code .

aschuch/AwesomeCache,aschuch/AwesomeCache