PR #60 identifiend a couple of issues in Kestrel that need fixing

[Tragetaschen]

Issues:

• Connections need to be tracked. Currently they are just new'ed without assigning them
• Reading from a socket doesn't distinguish between different kinds of errors (timeout / EOF / etc.)
• Empty catch blocks
• Consistent error handling
• Connections leak when closed by the client #61
• Active Keep-Alive connections are not closed before shutting down the loop #62
• Shutdown requests might free their memory before running the callback #63

With these, shutdown should work reliably and kept-alive connections shouldn't be an issue

Cleanup:

• Most libuv handle classes currently use a rather complicated protocol with new, a method call for more parameters
• Native resource cleanup should follow standard Dispose / finalizer logic
• Handling and calling the actual pinvoke delegates is convoluted
• Remove unsafe

[shhsu]

Just curious why this PR is closed. @Tragetaschen are you planning to rewrite a PR based on the current dev branch?