Merge branch 'release/2.12' into develop
prepare for next development iteration.
add javadoc
Maintenance pom.xml for publish central
add TimeZoneConverter for Spring framework.
Add comparison method to java.util.Date
add TimeZones class
各UTC定数を、TimeZones参照に変更。
Merge branch 'feature/supply_UTC_timezone_for_constant' into develop
add jackson2 serializers and deserializers
set version label to 2.13
Merge branch 'release/2.13'