Please add support for parsing with a text day-of-week

[mpenning]

If you google for "crontab every tuesday", the first hit is:

https://crontab.guru/every-tuesday

crontab.guru recommends using 0 0 * * TUE as the abbreviation, but this is not accepted by crontabula.

Please add support for three-letter text day-of-week, as recommended by crontab.guru and wikipedia.