New stat_cmds hook library initial commit.
Both stat-lease4/6-get commands implemented and unit tested

modified:
    configure.ac
    src/hooks/dhcp/Makefile.am
new:
    src/hooks/dhcp/stat_cmds/.gitignore
    src/hooks/dhcp/stat_cmds/Makefile.am
    src/hooks/dhcp/stat_cmds/stat_cmds.cc
    src/hooks/dhcp/stat_cmds/stat_cmds.dox
    src/hooks/dhcp/stat_cmds/stat_cmds.h
    src/hooks/dhcp/stat_cmds/stat_cmds_callouts.cc
    src/hooks/dhcp/stat_cmds/stat_cmds_log.cc
    src/hooks/dhcp/stat_cmds/stat_cmds_log.h
    src/hooks/dhcp/stat_cmds/stat_cmds_messages.mes
    src/hooks/dhcp/stat_cmds/tests/.gitignore
    src/hooks/dhcp/stat_cmds/tests/Makefile.am
    src/hooks/dhcp/stat_cmds/tests/run_unittests.cc
    src/hooks/dhcp/stat_cmds/tests/stat_cmds_unittest.cc
    src/hooks/dhcp/stat_cmds/version.cc