This is the second attempt.  The first attempt was
8a59ce6d and it failed.

This reverts commit 8a59ce6d.

Reported in https://github.com/nghttp2/nghttp2/issues/1384

Fix request stall if backend connection is reused and buffer is full.

Support building nghttpx with systemd using cmake

Run nghttpx integration test with cmake build.  Autotools build erases
artifacts for packaging tests, so we cannot run nghttpx integration
test with autotools build at the moment.

Relay on go modules to download dependencies.

nghttpx: Fix unchanged log level on configuration reload

Previously, if log-level is not mentioned in configuration file and
reload happens, the log level was not set to the default value NOTICE.
Instead, the log level stayed the same.  This commit fixes this bug.

Travis osx

Ignore Content-Length and Transfer-Encoding in 200 response to CONNECT request

A well known server sends content-length: 0 in 101 response.  RFC 7230
says Content-Length or Transfer-Encoding in 200 response to CONNECT
request: https://tools.ietf.org/html/rfc7230#section-3.3.3

It returns NULL if return value is HPE_OK.