added the six Webstack.jl repos to metadata

This pull request add the packages HttpCommon, HttpParser, HttpServer, WebSockets, Morsel, and Meddle.

* HttpCommon has types to represent HTTP requests/responses.
* HttpParser is a wrapper around Joyent's HTTP parsing library.
* HttpServer is a Http server using HttpCommon and HttpParser.
* WebSockets is an implementation of the WebSockets protocol compatible with HttpServer.
* Meddle is a middleware implementation over HttpServer and comes bundled with general purpose middleware like BodyDecoder and FileServer.
* Morsel is a Sinatra-like micro framework.