* Update `_expand` to lowercase each component of the expression.
* Fix _expand to reject int literals with underscores
* Fix combination of star and invalid expression bugs
* Security fix: fix overflow when using cron ranges
* Fix#155: raise CroniterBadCronError when error syntax
* Fix match when datetime has microseconds
* Added Python 3.8 and 3.9 support
OBS-URL: https://build.opensuse.org/package/show/devel:languages:python/python-croniter?expand=0&rev=30