[RELEASE] Released version 1.3.21

[RELEASE] Released version 1.3.21

Released version 1.3.21 with the following main changes :
    - [DOC] add missing rate_lim and rate_max
    - [BUG] check if rise/fall has an argument and it is > 0
    - [MINOR] add "description", "node" and show-node"/"show-desc", remove "node-name", v2
    - [DOC] Add information about http://haproxy.1wt.eu/contrib.html
    - [MINOR] acl: don't report valid acls as potential mistakes
    - [BUG] task.c: don't assing last_timer to node-less entries
    - [MINOR] export the hostname variable so that all the code can access it
    - [MINOR] stats: add a new node-name setting
    - [MINOR] acl: add support for hdr_ip to match IP addresses in headers
    - [CLEANUP] remove ifdef MSG_NOSIGNAL and define it instead
    - [BUG] buffer_forward() would not correctly consider data already scheduled
    - [MAJOR] http: add support for HTTP 1xx informational responses
    - [BUILD] stream_interface: fix conflicting declaration
    - [CLEANUP] include time.h from freq_ctr.h as it uses "now".
    - [MINOR] report list of supported pollers with -vv
    - [MEDIUM] new option "independant-streams" to stop updating read timeout on writes
    - [BUG] don't refresh timeouts late after detected activity
    - [MINOR] acl: add fe_conn, be_conn, queue, avg_queue
    - [BUILD] add a 'make tags' target (cherry picked from commit ebe0af4b77bca2042565a3f15fc1f597f5862874)