GitLab

 - many more parameters are now inherited from shared-network to subnet4
 - parameters now passed as const reference
 - it is no longer possible to specify echo-client-id on shared-network
   level (because it's a global parameter)
 - example config commented properly

    Merge branch 'trac5315_rebase'

    Replaced subnet-ids with subnets, and subnet-id with id in
    subnet commands text, and removed trailing whitespace in
    doc/guide/hooks.xml

 - Renamed SubnetIdIndexTag to avoid collision
 - Moved OptionDataParser to option_data_parser.cc|h
 - Updated hooks.xml to reflect recent changes