Parse Datetime Munger

A simpler, faster mungebit that takes Postgresql CreatedAt statements in the format of YYYY-MM-DD HH:MM:SS.SSSS and convert them into the choice of...
* days since 1970 (default)
* the hour of day (0-23, use `mode`="hod")
* the day of week (Mon-Sun, use `mode`="dow")
* the day of month (1-31, use `mode`="dom")
* the day of year (1-365, use `mode`="doy")
* the month of year (1-12 corresponding to Jan-Dec, use `mode`="moy")
* if the output is a holiday (`TRUE` or `FALSE`, use `mode`="holiday")
* if the output is a weekend (`TRUE` or `FALSE`, use `mode`="weekend")
* if the output is a business day (`TRUE` or `FALSE`, use `mode`="bizday")