document solving Embedded Experiences goal from charter

[tantek]

I have successfully used use of webmention.io's jf2 output + streams.tmb jf2 input (and subsequent HTML5+mf2 output) to do RSVPs embedding on my event posts (see indieweb.org/event#Tantek and indieweb.org/RSVPs#Tantek for links to examples) which is definitely an Embedded Experience per the description in the Chaarter Goals: https://www.w3.org/2013/socialweb/social-wg-charter.html#goals

jf2 should have a section on "implementation classes" (similar to other specs) with subsections such as "API endpoint" (webmention.io would qualify), and perhaps "Embedding Service" (streams.tmb would qualify) that describe how a standard embedding service can be built by consuming jf2, and producing stylable and presentable HTML+mf2 for providing Embedded Experiences