Swift 5.1 + Xcode 11

Upgrade Swift Tools version (5.1)

 - Migrate Package files to Xcode 11.
 - Remove images from project (in favor of Imgur).

Minor refactor around AESError

v1.0.3

AESError is now AES.Error

Refactoring & Enhancements

Kudos to the user Leo from SO:

• Favor Data(string.utf8) over string.data(using: .utf8)
• Remove stringToDataFailed error

Also added a Playground to make it easier to see the code in action.

Random iv is back

• Bring back random iv generation
• Remove NSData.bytes usage

First Release

Update AES.swift

Make `public data` otherwise `public init` isn't exposed