Source code documentation updates (#9)

This change adds documentation to quite a few existing public types that
didn't have a blurb before.

Additionally, this fixes a couple things that I think either didn't make
sense when going to document them:
- Rename ConnectionStream to VsockConnectionStream. This type only
functions for vsock connections.
- Deletes NsLock+Closure. This was not used anywhere.
- Rename ContainerizationOCI/Config.swift to ImageConfig.swift.

Signed-off-by: Danny Canter <danny_canter@apple.com>

Sources/ContainerizationIO/ReadStream.swift

@@ -18,6 +18,8 @@ import ContainerizationOS
 import Foundation
 import NIO
 
+/// `ReadStream` is a utility type for streaming data from a `URL`
+/// or `Data` blob.
 public class ReadStream {
     public static let bufferSize = Int(1.mib())