record the priority
[http2][refactor] use h2o_linklist_t for collecting streams
support listening unix domain socket.
[http2][wip] priority works!
fix spots pointed out from author.

 * use `struct sockaddr_storage` instead of `struct sockaddr_un`
 * use `port` and `type` instead of `unix:`
 * use `switch` statement
should use ${CMAKE_DL_LIBS} in place of -dl (fix #49)
add missing #include (fix #48)
remove unnecessary #include <alloca.h>
do not include alloca.h if it does not exist (it is included by default so that we could skip cmake on osx)
update the docroot in the example
add note to run h2o --help
Merge branch 'master' into kazuho/expr/http2-priority
merge minimum HTTP/2 priority impl. from kazuho/expr/http2-priority (#41)
report type that is neither "unix" nor "tcp" as error
add support for unix socket (merge branch 'kazuho/pr/45', close #45)