nghttpx: Fix path matching bug

Previously, if path is empty or path does not start with "/", nghttpx
did not try to match with wildcard pattern.  This commit fixes it.

Update nghttp2_session.c

Add missing free call on error in inflight_settings_new().

Support specifying stream priority via session::submit()

This commit adds 2 new options to handle X-Forwarded-Proto header
field.  The --no-add-x-forwarded-proto option makes nghttpx not to
append X-Forwarded-Proto value.  The
--no-strip-incoming-x-forwarded-proto option prevents nghttpx from
stripping the header field from client.

Previously, nghttpx always strips incoming header field, and set its
own header field.  This commit preserves this behaviour, and adds
additional knobs.

This reverts commit 8c0b2c68.

This reverts commit 6aa581d2.

This reverts commit 82b326e6.

Add section to promote the build from tar archives.

With --single-process option, nghttpx will run in a single process
mode where master and worker are unified into one process.  nghttpx
still spawns additional process for neverbleed.  In the single process
mode, signal handling is disabled.

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.