Lubridate verbs to be considered

[danzafar]

# Other functions that may be added in the future
#TODO: round_date
#TODO: ceiling_date
#TODO: rollback

# Parse date-times (composite functions)
#TODO: ymd_hms(), ymd_hm(), ymd_h()
#TODO: ydm_hms(), ydm_hm(), ydm_h()
#TODO: mdy_hms(), mdy_hm(), mdy_h()
#TODO: dmy_hms(), dmy_hm(), dmy_h()
#TODO: ymd(), ydm()
#TODO: mdy, myd
#TODO: dmy, dym
#TODO: yq
#TODO: hms, hm, ms

#TODO: date_decimal
#TODO: now
#TODO: today
#TODO: fast_strptime
#TODO: parse_date_time

#TODO: isoyear(), returns years according to the ISO 8601 week calendar.
#TODO: epiyear(), returns years according to the epidemilogical week calendars.
#TODO: isoweek
#TODO: epiweek
#TODO: qday()
#TODO: semester
#TODO: am
#TODO: pm
#TODO: dst
#TODO: leap_year
#TODO: update