The output format is similar to `hexdump -C`

Guaranteeing NULL-termination is very useful when name or value are
used with C functions which requires NULL-terminated string.

OpenSSL 1.0.2 is already released. Avoid the confusing wording that
seems to suggest that a development version of OpenSSL 1.0.2 provides
ALPN support.

For "http" or "https" URIs, :path header field must start with "/".
The only exception is OPTIONS method, which can contain "*" to
represent system-wide OPTIONS request.

It turns out that the cause of complication in backend request line
construction is a absolute-form in HTTP/1 request.  In HTTP/2, we have
separated pseudo-header fields and no problem at all.  In this commit,
we parse request URI in HTTP/1 frontend and extract values from it to
make backend logic simpler.  This patch removes host header field
emission in HTTP/2 backend if :authority is emitted.  It also rewrites
host header field with authority part in absolute-form URI as per RFC
7230.

... since gcc -pedantic warns on it.