6 part expression parsing incompatible with parse-crontab

[eshmu]

The way this module parses 6 part Cron expressions is incompatible with other heavily used Python modules like parse-crontab.

For example, the following Expression "* * * * * *" is described as "Every second" while parse-crontab treats it as "Every minute". This is because parse-crontab assumes the 6th star in this case is the year (and thus the expression contains minutes, hours, ..., years), while this module requires a 4 digit number in that slot to make the same assumption (and otherwise, assumes this is an expression containing seconds).

I'd like to suggest adding an option that would adopt the parsing convention of parse-crontab and thus make this module more compatible with other Python modules.

I'm happy to make the change and submit a PR.

[Salamek]

@eshmu PRs are welcomed