Cron expression parser and evaluator.

Allows for specifying cron - expressions (in Unix or Quartz like format) and evaluating when it will next match.

• cron-jodatime: Based on jodatime. Supports java6
• cron-java8: Based on java8/time. Requires java8+

See javadoc

• 2019-08-02: performance improvement when next time is further into the future (java8) by @n3world

• 2017-02-13: added support for java6 (supports android 4) by @adelnizamutdinov
• 2016-09-11: rewritten to Java 8 DateTime by @zemiak

• 2015-09-23: added timezone to tests by @alf

• 2015-08-05: added protection for endless loop when looking up Feb 30th & optional seconds by @michaelknigge