SETTINGS timeout is 10 seconds for now.

The nghttp2_submit_{request,response} family do not get this change.

These test tools uses JSON as input/output and could be handy
to produce compressed header blocks.

Use huffman table in https://github.com/grmocg/httpbis-header-compression

This change conveys better notion about compression context.

We use huffman encoding only when its encoded length is strictly less
than the original length.
As noted in the HPACK draft, the length of name/value is now 7-bit
prefix and its MSB is 1 if the following string is huffman encoded.

So that we can preserve leading bits.

Conflicts:
	lib/nghttp2_hd.c