added timeoutInterval param to upload methods

Added async upload method

NKHttp.upload now lets you change the image compression quality

Callback methods do not throw anymore

NetworkKit now uses SwiftPlus 1.1.1

NetworkKit now depends on SwiftPlus 1.1.0

made async functions only available for iOS, watchOS, tvOS and macOS

Added documentation, postObject callback now only returns object and …

…postObjectArray callback only array