Hi there!

First of all - awesome library - easy to use, easy to extend.

So I'm myself working with the crontab format and I found it would be awesome if this library would support more complex steps for hours, minutes and basically every field.

What is already working are these step definitions: '*/10' aka 'every 10 minutes'
What is defined in the crontab manual, but does not work are steps with ranges:

• '5-20/5' - every 5th minute from 5 through 20
• '5/5' - every 5th minute from 5 through 59

The ReactJS Cron library already supports that as far as I see. And whithout considering the UI for it, it probably already is quite simple.

As a note:
Initially I thought about implementing it myself for my use case in my project, but found that the Segment Factories are not exported in the index.ts, and without them it is quite tedious to extend e.g. the minute field. So that would also be awesome!

Thanks in advance :) And once again awesome library.