Yes of course, if there's something that can be fixed and/or improved, I'm always interested. However the HTTP implementation in SFML is not meant to be the most complete one ever, it focuses on the most common stuff.
I don't know all the details about HTTP 1.1 and 1.0, so maybe you can help me. What exactly do you think that SFML should support? What do the 100 and 101 statuses mean, when are they sent?
The 100 status is "Continue", and can be ignored.
More:
http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.1.1The 101 status is "Switching Protocols", it is normally sent when the client has requested to upgrade the protocol to a secure connection (https) from what I've read.
More:
http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.1.2Client "Upgrade" command:
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.42The entire HTTP/1.1 reference can be read at
http://www.w3.org/Protocols/rfc2616/rfc2616.html , but it's a bit overwhelming to try to do all at once. I would begin with those two statuses, maybe chunked transfer encoding if you haven't already, and commonly used client headers (Accept [used to describe what types of responses the client is looking for, and order of preference], Upgrade, Referer, User-Agent [to differentiate between IE, Firefox, Chrome, SFML, etc], and If-Modified-Since [used to hold a client-side cached page]), and support for compressed response bodies (Content-Encoding response header, either "compress" LZW or "gzip" LZ77 compression).
PS: That said, I'm looking at the HTTP/1.0 reference right now, and SFML actually has most of it. Only thing really missing is request parameters.