Previously, the number of stream in one dependency tree (not including
root) is limited to 120.  This is due to the fact that we use
recursive calls to traverse trees.  Now we replaced recursive calls
with loop, we can remove this limitation.  Also now all streams are
descendant of root stream, rather than linked list of individual
subtree root.

Merge branch 'openssl_no_ec' of https://github.com/yuki-kodama/nghttp2 into yuki-kodama-openssl_no_ec

The overall meaning is the same. I added a paragraph to introduce nghttp2_hd_inflate_hd(), and added an explanation of using NGHTTP2_NV_FLAG_NO_INDEX for security sensitive headers.

This fixes 2 things:
1. potential busy loop
2. disabling ticket is not working after resumption