[RELEASE] Released version 1.5.9

Released version 1.5.9 with the following main changes :
    - BUILD: fix "make install" to support spaces in the install dirs
    - BUG/MEDIUM: checks: fix conflicts between agent checks and ssl healthchecks
    - BUG/MEDIUM: ssl: fix bad ssl context init can cause segfault in case of OOM.
    - BUG/MINOR: samples: fix unnecessary memcopy converting binary to string.
    - BUG/MEDIUM: connection: sanitize PPv2 header length before parsing address information
    - BUG/MEDIUM: pattern: don't load more than once a pattern list.
    - BUG/MEDIUM: ssl: force a full GC in case of memory shortage
    - BUG/MINOR: config: don't inherit the default balance algorithm in frontends
    - BUG/MAJOR: frontend: initialize capture pointers earlier
    - BUG/MINOR: stats: correctly set the request/response analysers
    - DOC: fix typo in the body parser documentation for msg.sov
    - BUG/MINOR: peers: the buffer size is global.tune.bufsize, not trash.size
    - MINOR: sample: add a few basic internal fetches (nbproc, proc, stopping)
    - BUG/MAJOR: sessions: unlink session from list on out of memory