logger: add --sd-id and -sd-param

logger: add --sd-id and -sd-param

This patch add support for RFC 5424 structured data elements. For
example:

     logger --rfc5424 --sd-id zoo@123                \
                      --sd-param tiger=\"hungry\"    \
                      --sd-param zebra=\"running\"   \
                      --sd-id manager@123            \
                      --sd-param onMeeting=\"yes\"   \
                      "this is message"

produces:

     <13>1 2015-10-01T14:07:59.168662+02:00 ws kzak - - [timeQuality tzKnown="1" isSynced="1" syncAccuracy="218616"][zoo@123 tiger="hungry" zebra="running"][manager@123 onMeeting="yes"] this is message

Signed-off-by: Karel Zak <kzak@redhat.com>