Add more core support(s)

[harsath]

We need to implement the following,

• [x] The HTTP HEAD method requests the headers that would be returned if the HEAD request's URL was instead requested with the HTTP GET method. Add HEAD support
• [ ] REST API Endpoint's resource GET(right now, we only support endpoints for POST), and later an option for HTTP Basic Auth for such endpoints.
• [x] (extended) We need to make a desition before creating HTTPGETREsponseHandler and HTTPPOSTResponseHandler to check for the REST API's endpoint and callback fn. And make choices accordingly(possible solution?)
• [x] HTTPMessage building raw-message's SetResponseType must be determined from SetResponseCode, We need to avoid manually settingup the string value on downstream.
• [ ] Think about Network-Transport independent way of handling the HTTP/1.1(read the specification and std-impls)

[harsath]

For point 2, (REST-APIs resource GET), I think this is an application's business logic and we as a server DO NOT need to worry about this. We will parse the HTTP-Message and pass it to the corresponding call-back handler, and it is the handler's responsibility to take care of this business logic. But I think, we can support the HTTP Basic Auth for such endpoints.

Draft: Let the user pass the file containing the username/password for the HTTP Basic Auth and we just dobase64 decode and check against those files. If it gets a hit, we will send the parsed HTTP-Message object to the call-back handler if not, we will send an HTTP Not Authorized.

[harsath]

We need to create a few template responses HTTP::HTTPMessage for a common types of responses like error code, Auth-fail, and such. Since the actual implementation code and client's examples get longer for no reason, we need to find some way to abstract out those templates.

EDIT: Done

[harsath]

Support for UNIX domain listener. Why? Because we can have web servers like NGINX as a frontend server/reverse proxy to our C++ runtime which processes the HTTP Messages from that UNIX domain sock's endpoint and write the processed response to the NGINX's socket. Make NGINX do certain heavy lifting like SSL, Timeouts and we just focus on the business logic.