Swift-Sodium

Only the files for the swift package have been kept.

• The struct named Sodium has been renamed SodiumSwift to fix the generated .swiftinterface.
• We use @_implementationOnly import Clibsodium ti hide Clibsodium.
• SecretStream.PullStream and SecretStream.PushStream are not private to hide Clibsodium. If those classes are needed later publicly, they can be wrapped.