[RELEASE] Released version 1.5.7

Released version 1.5.7 with the following main changes :
    - BUG/MEDIUM: regex: fix pcre_study error handling
    - BUG/MINOR: log: fix request flags when keep-alive is enabled
    - MINOR: ssl: add fetchs 'ssl_c_der' and 'ssl_f_der' to return DER formatted certs
    - MINOR: ssl: add statement to force some ssl options in global.
    - BUG/MINOR: ssl: correctly initialize ssl ctx for invalid certificates
    - BUG/MEDIUM: http: don't dump debug headers on MSG_ERROR
    - BUG/MAJOR: cli: explicitly call cli_release_handler() upon error
    - BUG/MEDIUM: tcp: fix outgoing polling based on proxy protocol
    - BUG/MEDIUM: tcp: don't use SO_ORIGINAL_DST on non-AF_INET sockets