src/bin/dhcp6/json_config_parser.cc
        createGlobalDhcp6ConfigParser()
        - added clause to invoke new D2ClientConfigParser to
        set staging config
        - added clause to apply staged D2ClientConfig (formerly done
        by parser commit

    src/bin/dhcp6/parser_context.h
    src/bin/dhcp6/parser_context.cc
        aded PARSER_DHCP_DDNS context

    src/bin/dhcp4/simple_parser6.h
    src/bin/dhcp4/simple_parser6.cc
        defined SimpleParser6::D2_CLIENT_CONFIG_DEFAULTS
        SimpleParser6::setAllDefaults() - now sets defaults
        for D2ClientConfig

    src/bin/dhcp6/tests/d2_unittest.cc
    src/bin/dhcp6/tests/fqdn_unittest.cc
        Updated replace-name-mode values and tests
        (true/false no longer supported)

    doc/guide/dhcp6-srv.xml
        Updated, replace-client-name no longer accepts booleans

 - The parsers converted to SimpleParser
 - Unit-tests updated, cleaned up and corrected
 - Updated examples to actually use the information
 - Updated User's Guide that the empty mac-sources is not allowed

 - There's new section Kea Libraries

 - address_family_, default ctor removed from two parsers
 - copyright year updated
 - Element::getNonConst is now documented
 - user's guide is now clear about csv-format default value is now true

 - clarified JSON usage in admin guide (True/False not allowed)
 - fixed incorrect reference to hosts4-storage
 - clarified that empty mac-sources entry is not allowed
 - added extra text about syntactic contexts
 - corrected several typos

- Extended description of the S46 Rule Option
- Added Lightweight 4over6 to the softwire examples
- Updated Supported DHCPv6 standards with RFC6334
- Updated DHCPv6 spec file

This change includes the code implemented by the pull request
submitter as well as Marcin's fixes/changes on top of it, but
without a review.