Add more "Web surface" concepts

[dret]

right now the only concepts supported are media types, HTTP header field types, and link relation types. There definitely should be HTTP status codes as well. This issue serves to capture ideas about additional concepts that "belong into the web surface" and should be documented in a similar way as media types, HTTP header field types, and link relation types are documented right now.

[dret]

this is presented as a 5in5 talk at the WS-REST workshop: https://github.com/apiacademy/WSREST2016/wiki/Web-Surface; the WS-REST 2016 discussion identified the following concepts that could be added to the list above:

• HTTP Status Codes
• HTTP Request Methods
• Content Encodings

[dret]

another inspiration for additional web surface coverage are HTTP cache control extensions from @comcast-jonm's API360 talk. one example is this RFC: https://tools.ietf.org/html/rfc5861

[dret]

for the cache control extensions, the relevant IANA registry of "HTTP Cache Directives" is here: http://www.iana.org/assignments/http-cache-directives/http-cache-directives.xhtml

[dret]

the proposals made so far have their own issues now (#14 #15 #16 #17). this issue will remain open as a general discussion topic for adding even more concepts beyond those identified so far.

[dret]

not mentioned here originally, but the (old) issue #4 falls into this generic one as well.

[dret]

#5 qualifies as well, but is based on a long-expired draft, so probably not (yet) ready for prime time.

[dret]

almost done with this one, just a few more #22 values to add.

[dret]

this issue was resolved a while ago. new concepts should be requested as individual issues.