- created new table with supported RAI suboptions
 - added RFCs 3011, 3993
 - removed outdated reference do 1497 from limitations section

- replaced all occurences to old_cltt and old_valid_lft in unittests
- renamed syncInternalTimestamp to syncExistingLifetime and changed order
of parameters
- renamed updateInternalTimestamp to updateExistingLifetime
- updated doxygen
- added extra check for all occurences of deleteLease (either call
EXPECT or ASSERT), and only use cast to void if explicitly specified
- updated ChangeLog
- updated old_cltt and old_valid_lft on fromElementCommon and added
unittests
- throw exception with different message on memfile with persitence
disabled for easier debugging

Regenerated parsers for kea-dhcp4/6 for !976

src/bin/dhcp4/dhcp4_lexer.cc
src/bin/dhcp4/dhcp4_parser.cc
src/bin/dhcp4/dhcp4_parser.h
src/bin/dhcp4/location.hh
src/bin/dhcp4/position.hh
src/bin/dhcp4/stack.hh

src/bin/dhcp6/dhcp6_lexer.cc
src/bin/dhcp6/dhcp6_parser.cc
src/bin/dhcp6/dhcp6_parser.h
src/bin/dhcp6/location.hh
src/bin/dhcp6/position.hh
src/bin/dhcp6/stack.hh

doc/examples/kea4/all-keys.json
doc/examples/kea6/all-keys.json
doc/sphinx/arm/dhcp4-srv.rst
doc/sphinx/arm/dhcp6-srv.rst
src/lib/dhcpsrv/network.h
src/lib/dhcpsrv/tests/dhcp_parsers_unittest.cc
    fixed typos