First Beta of soon to be stable version

What's Changed

• Replace ExtendedCronInterval with extended property by @maennchen in #18
• Rename CronInterval to CronExpression by @maennchen in #19
• Rename Modules to better names by @maennchen in #20
• Cleanup Helper Functions by @maennchen in #21
• Move helper function from Crontab to Crontab.Scheduler, enforce naming conventions by @maennchen in #22
• Cron Expression Sigil by @maennchen in #23
• Improve Documentation by @maennchen in #24
• Rename Various variables to cron_interval by @maennchen in #25
• Credo Fixes by @maennchen in #26
• Improve types by @maennchen in #27

Full Changelog: v0.8.5...v1.0.0-beta.1