Add cron script for scheduling commands

cron/Help.txt

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+Cron
+
+Cron allows a user to schedule commands to run at some point in the future.
+Jobs can be scheduled based on the turn tracker or clock time (relative to now
+or at some specific time in the future), and can optionally recur at a specified
+interval.  Each job is given a unique ID, which can be used to remove it at a
+later time.
+
+It is recommended that this script be used in conjunction with the CommandShell
+module, which will improve output formatting and command discovery.
+
+
+Commands:
+
+The "cron" command operates in several modes:
+
+    !cron [options] command
+	Schedules the specified command to be run later.  Available options are
+	described in detail below.
+
+    !cron -l
+	Lists all scheduled jobs.
+
+    !cron -R job_ID ...
+	Removes one or more scheduled jobs.
+
+The "cron" command accepts the following options:
+
+    -h, --help			Displays a help message and exits.
+
+    -r N, --rounds N		The first execution of the command will be in N
+				rounds.  If an initiative count is not specified
+				(see below), the current count will be used, or
+				0 if none is available.  Cannot be used with
+				time-based arguments.
+    -c N, --count N		The command will execute on initiative count N.
+				If the number of rounds in the future is not
+				specified (see above), it will default to the
+				next time the specified count comes up.  Cannot
+				be used with time-based arguments.
+    -t T, --time T		The first execution of the command will be at
+				time T (HH:MM:SS).  If not all values are given,
+				zeroes will be added to the smaller end (e.g.
+				"1:23" will be interpreted as "1:23:00").  Times
+				will be interpreted to be within the next
+				24 hours.  Cannot be used with initiative-based
+				arguments.
+    -a T, --after T		The first execution of the command will be after
+				interval T (HH:MM:SS).  If not all values are
+				given, zeroes will be added to the larger end
+				(e.g. "1:23" will be interpreted as "00:01:23").
+				Cannot be used with initiative-based arguments.
+    -i I, --interval I		The command will be repeated every I rounds or
+				I time (HH:MM:SS).  If rounds or count is given,
+				or if I is a single number, I will be considered
+				a number of rounds.  Otherwise, I will be
+				considered as a time interval, with zeroes added
+				to the larger end to fill missing values (e.g.
+				"1:23" will represent 1 minute and 23 seconds).
+				If no first execution time is specified, the
+				first execution will be I rounds or seconds in
+				the future.
+    -f USER, --from USER	The command will be executed as USER.  This need
+				not be a player or character in the game.
+
+    -l, --list			List all scheduled jobs.
+
+    -R, --remove		Remove all specified jobs.  All other arguments
+				will be considered job IDs (so multiple jobs
+				can be removed with one command like
+				"!cron -R 1 5 8").
+
+
+Examples:
+
+!cron -r 10 The bomb's timer reaches zero!  It explodes for [[10d10]] damage.
+    Called on the initiative count in which the bomb's timer is set, it will
+    explode in 10 rounds.
+
+!cron -c 12 -i 1 -f "Hey, eejit!" /w gm Don't forget the spider's turn
+    A forgetful GM might use this subtle reminder that the party's mage summoned
+    a spider which acts on the mage's initiative count (12, in this example).
+
+!cron -f "Acid Rain" -i 1 The acid burns for [[2d6]] damage.
+    Inline roll results are stripped from the command and replaced with the
+    original roll expression.  Long story short: the above gives a new damage
+    roll each round.
+
+!cron -f Nanny -t 23:00 Bedtime for sleepy-head.  Time to wrap things up.
+    Be aware that the time zone is based on the API server, not the client who
+    runs the command.
+
+!cron -a 30 Hey!  It's 30 seconds later than when I typed this.
+    Probably more useful with larger delay amounts.
+
+!cron -t 0:00:00 -i 1:00:00 /desc The clock chimes.
+    This will fire every hour, on the hour.  (Can also just do "-t 0").