Added a Podspec so we can use your project with Cocoapods.

Hi Diego,

Great project, it's exactly what we needed. 

We use [Cocoapods](http://cocoapods.org) to manage our dependencies, so I created a podspec for your project.

With this new podspec, anyone can include

    pod 'KeyValueObjectMapping', :git => "https://github.com/dchohfi/KeyValueObjectMapping.git"

in their Podfile to use KVObjectMapping in their projects.

Cheers! :)
-V