TD2c in set_tradingdays

[AQLT]

The TD2c option seems missing from the set_tradingdays(option=) parameter.
Maybe we should also enable the TD2 option (for working days) and TD7 (for tradingdays) adding those options in:

rjd3toolkit/R/spec_regarima.R

Lines 1023 to 1025 in e44c1ea

	option <- match.arg(toupper(option)[1],
	choices = c("TRADINGDAYS", "WORKINGDAYS", "NONE","USERDEFINED",
	"TD3", "TD3C", "TD4", "HOLIDAYS"))