Android / Linux Support #149

Provide Android and Linux Support. We obviously won't be able to import Security, Network, or SwiftUI modules so we'll need to wrap these imports in macros with libs provided by the Core Libs Foundation as well as any code specific paths.

See Getting Started with the Swift SDK for Android

#if canImport(CryptoKit)
import CryptoKit
#else
import Crypto
#endif

To compile we'll need to do the following:

swift build --swift-sdk aarch64-unknown-linux-android28