Add preliminary AESCrypt.podspec file

Hi Gurpartap
I recently used `AESCrypt` on a personal project and I'm using [CocoaPods](http://cocoapods.org/) for managing dependencies.

I created an `AESCrypt.podspec` file if you're interested in getting `AESCrypt` into CocoaPods and maintaing it in your repo.

If you don't mind I'd also like to submit the podspec to https://github.com/CocoaPods/Specs.

#### Notes

* CocoaPods suggest that a library should be versioned. `0.0.1` is acceptable for a first submission. But it's preferred that you choose a version number and tag it in the repo.
    * If you do, then `:tag => 'tagname'` should be used instead of `:commit => 'commitsha'` in the podspec
    * See https://github.com/CocoaPods/Specs/wiki/%22Please-add-semantic-version-tags%22-issue-template if you're interested