Request: Add ``season`` as an option for the unit argument ``floor_date``

[kendonB]

Would work like:

floor_date(as_date("2014-01-01"), unit = "season")
#> [1] "2013-12-01"

[kendonB]

A workaround:

date <- today()
floor_date(floor_date(date, "month") + months(1), unit = "quarter") - months(1)
#> [1] "2017-03-01"