Addressed a myriad of minor typos and wording issues.

modified:
ChangeLog
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/bin/dhcp4/dhcp4_srv.cc
src/bin/dhcp4/tests/config_parser_unittest.cc
src/bin/dhcp4/tests/fqdn_unittest.cc
src/bin/dhcp6/tests/config_parser_unittest.cc
src/bin/dhcp6/tests/d2_unittest.cc
src/bin/dhcp6/tests/fqdn_unittest.cc
src/lib/dhcpsrv/alloc_engine.cc
src/lib/dhcpsrv/alloc_engine.h
src/lib/dhcpsrv/d2_client_cfg.h
src/lib/dhcpsrv/parsers/base_network_parser.cc
src/lib/dhcpsrv/srv_config.h