Get 0.2.0

• It now supports iOS 13, macOS 10, watchOS 6, and tvOS 13
• Make willSend async - #11, thanks to Lars-Jørgen Kristiansen
• Add a more convenient way to initialize APIClient (same as ImagePipeline in Nuke):

let client = APIClient(host: "api.github.com") {
    $0.delegate = MyClientDelegate()
    $0.sessionConfiguration.httpAdditionalHeaders = ["apiKey": "easilyExtractableSecretKey"]
}

• You can now provide a session delegate (URLSessionDelegate) when instantiating a client for monitoring URLSession events – the client will continue doing its thing
• Add metrics (URLSessionTaskMetrics) to Response
• Add public Response initializer and make properties writable