Add section to promote the build from tar archives.

This commit adds 2 new options to handle X-Forwarded-Proto header
field.  The --add-x-forwarded-proto option makes nghttpx append
X-Forwarded-Proto value.  The --strip-incoming-x-forwarded-proto
option makes nghttpx to strip the header field from client.

Previously, nghttpx always strips incoming header field, and set its
own header field.  This commit changes this behaviour.  Now nghttpx
does not strip, and append X-Forwarded-Proto header field by default.
The X-Forwarded-For, and Forwarded header fields are also handled in
the same way.  To recover the old behaviour, use
--add-x-forwarded-proto and --strip-incoming-x-forwarded-proto
options.

The namespace shrpx::ssl was also renamed as shrpx::tls.

nghttp2::ssl namespace was also renamed as nghttp2::tls.

Previously, we drop connection if server certificate verification
fails after handshake.  With this commit, we fail handshake if that
happens.

This reverts commit b4337d1b.

nghttpx: Retry getaddrinfo without AI_ADDRCONFIG

Escape access log

src: BoringSSL supports SSL_CTX_set_{min,max}_proto_version.

The certain characters coming from client are now escaped with "\xNN"
where NN is the ascii code of the character in hex notation.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

asio: client: Send PING after 30 seconds idle