Make HttpServer more consistent with WebSocketServer

[Rohansi]

This makes HttpServer more consistent with WebSocketServer by adding missing constructor overloads and properties.

• Adds constructor overloads enabling listening on specific IP addresses
• Adds a constructor to get listen parameters from a URL string
• Fixes a missing null check for IPAddress parameters in WebSocketServer
• Fixes an error that prevented HttpServer from sending error messages (HttpConnection.cs)

[sta]

Hello there, thanks for your pull request.

I plan to merge this manually by inches, adding some changes.

And when i merge your code, i will add a contributor info such as below. Is it okay?

/*
 * Contributors:
 * - Rohan Singh <[email protected]>
 */

[Rohansi]

Yes, that's fine. Thanks.

[Rohansi]

Any progress on this?

[sta]

Not yet. Hold on please.