Reset status = 0 when entering s_status state in htparse_run

Set -n default value to 1. Show missing default values.  Use -c value
in SPDY session.

Require Libevent-openssl 2.0.8 because we use
evconnlistener_set_error_cb().

htparse is written by Mark Ellzey and part of libevhtp.
https://github.com/ellzey/libevhtp

The included code are modified by me for bugfixes.
See my fork:
https://github.com/tatsuhiro-t/libevhtp/tree/master/htparse

I think spdylay supports writing only partial frames.

The default log level is now WARNING.

Put libhtparse in examples/htparse