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- 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.

Removed a todo, updated example with multiple options and added
item descriptions in the DHCPv6 spec file.

 - added vendor options example and made it out-of-pool in
   kea6/reservations.json
 - fixed couple indents in dhcp{4,6}-srv.xml
 - added enclosing subnet4 where it was missing in examples
 - renamed section dedicated to option reservations
 - default value of host-reservation-identifiers presented
   differently

# Conflicts:
#	doc/examples/kea4/backends.json

This is a result of the review. This change was suggested so as
the order of lease expiration specific parameters follows the
order in which they are described.

looks like same typo was repeated to different files

Also, renamed interface-config to interfaces-config (plural form).

 - eth0 => ethX in several examples
 - added @todo in Dhcp6Srv, getMAC() is now static
 - added @todo in CfgMACSource

 - clarified that order in mac-sources is important
 - tweaked all examples to use eth9 rather than more common eth0

 - logger names are now kea-dhcp4, kea-dhcp6, kea-dhcp-ddns
 - fix in keactrl_tests
 - User's Guide, examples updated