HPACK examples.

We've found a bug (now fixed) in the javascript implementation used to
generate the examples for HPACK-04 (the expiry mechanism was erroneously a
stack instead of a fifo).

Thankfully, the examples didn't use enough space to trigger the bug, and so
should be correct.

Next draft will include expiry amongst other things.
An issue w.r.t. improving corner-case coverage for examples is tracked
here: 297 <https://github.com/http2/http2-spec/issues/297>

I'd greatly appreciate any other opinions about improving the output
editorially.
Is it too much information? To little? Can it be better formatted (yes.. oh
yes.. but how)?
-=R